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Screening Assessment for

Pseudomonas aeruginosa (ATCC 31480)
Pseudomonas aeruginosa (ATCC 700370)
Pseudomonas aeruginosa (ATCC 700371)

Environment Canada
Health Canada

June 2012

(PDF Version - 599 KB)

Table of Contents


Pursuant to paragraph 74(b) of the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of Environment and of Health have conducted a screening assessment on three strains of Pseudomonas aeruginosa(ATCCstrains 31480, 700370 and 700371). These strains are listed on the Domestic Substances List (DSL) thus indicating that they were added to the DSL under Section 105 of CEPA 1999 because they were manufactured or imported into Canada between January 1, 1984 and December 31, 1986 and they entered or were released to the environment without being subject to conditions under CEPA 1999 or any other federal or provincial legislation.

The species Pseudomonas aeruginosa is generally considered a ubiquitous bacterium, occurring naturally in many environmental media; P. aeruginosa is probably one of the most widespread of all bacterial species. It has the ability to adapt to and thrive in many ecological niches especially those that are moist. The species possesses characteristics that allow for multiple potential uses in various industrial and commercial sectors. These include waste degradation (particularly in oil refineries), textile, pulp and paper, mining and explosives industries, as well as in commercial and household drain cleaners and degreasers, septic tank additives and general cleaning products and odour control products.

P. aeruginosa is recognized as a Risk Group 2 pathogen by the Canadian Food Inspection Agency (Animal Pathogen Import Program), and requires a permit in order to be imported to Canada. Generally, Risk Group 2 pathogens are any pathogens that can cause disease but, under normal circumstances, are unlikely to be a serious risk to healthy organisms in the environment. If needed, effective treatment and preventive measures are available, and the risk of spread is limited.

Information from the scientific literature indicates that this micro-organism has pathogenic potential in both otherwise healthy and immunocompromised humans. P. aeruginosa is recognized by the Public Health Agency of Canada as a Risk Group 2 human pathogen. It has the ability to spread and acquire antibiotic resistance genes which may compromise the effectiveness of antibiotics that are currently used for the treatment of P. aeruginosa infections. P. aeruginosa produces a wide variety of extracellular enzymes and toxins that are important factors for its pathogenicity in susceptible humans.

To establish whether living organisms on the DSL continue to be manufactured in or imported into Canada, a notice was issued pursuant to paragraph 71(1)(a) of the CEPA 1999. There were no reports of industrial activity (import or manufacture) with respect to these substances in Canada for the specified reporting year of 2008. These results indicate that in 2008, the three DSL-listed strains of P. aeruginosa (31480, 700370 and 700371) were not imported or manufactured and therefore the likelihood of exposure to these substances in Canada resulting from commercial activity is low.

Based on available information, and until new information is received indicating that these substances are entering, or may enter, the environment from commercial activity or from other anthropogenic sources, it is proposed that the above substances are currently not entering or likely to enter the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or constitute a danger to the environment on which life depends or that constitute a danger in Canada to human life or health. Therefore, it is proposed that these substances do not meet any of the criteria as set out in section 64 of CEPA 1999.

However, should exposure increase through new activities, there is a potential risk to human health and the environment based on the pathogenicity and toxicity of P. aeruginosa to susceptible humans and non-human species. Therefore, there is concern that new activities for the above substances which have not been identified or assessed under CEPA 1999 could lead to the substances meeting the criteria as set out in section 64 of the Act. Therefore, it is recommended that the above substances be subject to the Significant New Activity provisions specified under subsection 106(3) of the Act, to ensure that any new manufacture, import or use of these substances will undergo ecological and human health assessments as specified in section 108 of the Act, prior to the substances being considered for introduction into Canada.

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Pursuant to paragraph 74(b) of the Canadian Environmental Protection Act, 1999 (CEPA 1999), the Ministers of Environment and of Health are required to conduct screening assessments of those living organisms listed on the Domestic Substances List (DSL) to determine whether they present or may present a risk to the environment or human health (according to criteria as set out in section 64 of CEPA 1999). These living organisms were nominated and added under the DSL under Section 105 of CEPA 1999 because they were manufactured or imported into Canada between January 1, 1984 and December 31, 1986 and they entered or were released into the environment without being subject to conditions under CEPA 1999 or any other federal or provincial legislation.

Screening assessments examine scientific information and develop conclusions by incorporating a weight-of-evidence approach and precaution. This screening assessment considered hazard information obtained from the public domain as well as from unpublished research data and from internal and external experts. Exposure information was also obtained from the public domain as well as information from a mandatory CEPA 1999 s. 71 Notice published in the Canada Gazette Part 1 on October 3, 2009. Further details on the risk assessment methodology used are available in the Risk Assessment Framework document titled “Framework on the Science-Based Risk Assessment of Micro-organisms under the Canadian Environmental Protection Act, 1999”.

Data that are specific to the three DSL-listed P. aeruginosa strains (ATCC 31480, ATCC700370, ATCC 700371) are identified as such. Where data concerning the three particular strains were not available, surrogate information from literature searches of both P. aeruginosa and the genus Pseudomonas was used. Surrogate organisms are identified in each case to the taxonomic level provided by the source. Information identified as of June 2010 was considered for inclusion in this report.

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1. Hazard Assessment

A hazard assessment characterizes the micro-organism (Section 1.1) and identifies the potential adverse effects on the environment and/or human health and the extent and duration of these effects (Section 1.2). The hazards may be posed by the micro-organism itself, its genetic material or its toxins, metabolites or structural components.

1.1 Characterization

1.1.1 Taxonomic Identification and Strain History

The accurate taxonomic identification of a micro-organism is essential in distinguishing pathogenic from non-pathogenic species and strains. A polyphasic approach combining classical microbiological methods relying on a mixture of traditional tools (such as culture-based methods) and molecular tools (such as genotyping and fatty acids analysis) is often required.

Pseudomonas aeruginosa is a Gram-negative, motile, rod-shaped bacterium. Information regarding colony morphology of the DSL-listed P. aeruginosa strains and ATCC 31479, the parental strain of ATCC 31480, is outlined in Table 1.

Table 1: Selected colony morphology of ATCC strains 31479, 31480, 700370 and 700371

ATCC #ShapeSize (mm) DiameterMarginElevationColourOpacityPigment
31479[*]slightly irregular3-6wrinkled-undulateflatwhiteslightly opaquefluorescent yellow
31480[†]circular10undulateraisedoff-white/ colourlessopaquediffusible green-blue
700370[†]circular8entire-undulateraised - slightly umbonatetan–goldopaque with translucent ringsdiffusing green
700371[†]irregular6entire-undulateraisedoff-white/light beigesemi-translucentcolourless translucent material that extends beyond the described colony
[*] Data from US Patent #4,288,545, P. aeruginosa appearance of colony on TSB agar after 48h at 35°C.
[†] Data generated by Health Canada’s Healthy Environments and Consumer Safety Branch. Refer to Appendix 1B for a summary of the three DSL-listed strains’ growth kinetics on different media at 28°C and 37°C.

Table 2 outlines various aspects of taxonomic identification and strain history for DSL-listed P. aeruginosa strains ATCC 31480, ATCC700370 and ATCC 700371. Strain HCP (ATCC 31479) is the parent strain that was chemically mutated to generate strain ATCC31480. BIOLOG and API were used to identify the strains as P. aeruginosa. These approaches provided consistent results for the biochemical identification of various P. aeruginosaisolates based on the results generated from Health Canada’s Double Blind International Cooperative Study for the Identification of Pseudomonas Species (Micah Krichevsky, personal communication, 2010).

Additional data generated by Health Canada on growth kinetics at different temperatures (Appendix 1A), growth on different media at 28ºC and 37ºC (Appendix 1B) and fatty acid methyl-ester (FAME) analysis (Appendix 1C), provided further confirmation of the identification. It should be noted that these techniques can not be used to differentiate the DSL-listed strains from other P. aeruginosa strains.

Table 2: Taxonomic identification and strain history

 ATCC 31479ATCC31480[*]ATCC700371[*]ATCC700370[*]
Identification MethodNDBIOLOG, FAME[x]and AFLP marker[†]BIOLOG, FAME[x]and APIBIOLOG, and FAME[x]
Original Sourcesoil from Salem, Virginia, USAmutant of parent strain ATCC 31479environmentenvironment
Isolated for:N/Aits synergistic activity with other bacteria in degradation of oleaginous materials in wastewaterbiodegradation propertiesoxidation properties
ModificationsN/Amutated from the parent strain ATCC 31479 using 0.2% 8-azaguanine in a bench-top biotower; selective pressure from pentachlorophenolnonenone
ND no data
N/A not applicable
[*] Obtained from Spraker, 1981 and DSL Nomination Form B (confidential business information)
[x] FAME data was generated by Health Canada’s Healthy Environments and Consumer Safety Branch (see Appendix 1C)
[†] Generated by Environment Canada (Xiang et al., 2010)

Genotypic methods, such as full genomic sequencing (Stover et al., 2000)(Ivanova et al. 2003), multi-locus sequence typing (MLST) (Khan et al., 2008; Curran et al., 2004), and terminal restriction fragment length polymorphism (T-RFLP) profiling of the 16S–23S rRNA internal transcribed spacer (ITS1) gene region (Spasenovski et al., 2009) have been extensively used to demonstrate the phylogenetic relationships and the genomic variations among clinical and environmental isolates of P. aeruginosa. 16S rDNA sequence analyses of the three DSL P. aeruginosastrains, conducted by Health Canada, have shown greater than 99% homology (less than 10 base pairs difference) compared to other P. aeruginosaisolates on the proprietary MicroSeq ® ID library (ATCC 10145, ATCC27853, ATCC 25619). This data set shows that the 16S rDNA from test DSL strains in this study have been matched at the level of genus and species. DSL P. aeruginosa 16S rDNA sequences also show high similarity when compared to published P. aeruginosa sequences in NCBI-Blast (National Center for Biotechnology Information- Basic Local Alignment Search Tool).

Studies have suggested that some P. aeruginosa clinical isolates are phenotypically, genotypically, chemotaxonomically and functionally indistinguishable from environmental isolates, such as the three DSL-listed strains. Römling et al. (1994) reported that a clone frequently isolated from cystic fibrosis patients was also detected at a high frequency in aquatic environments, and Alonso et al. (1999) reported that both oil-contaminated soil isolates and clinical isolates of P. aeruginosa show pathogenic and biodegradative properties. Wolfgang et al. (2003) reported that the genomes of P. aeruginosa strains, representing distinct clinical or environmental sources, are highly conserved. The genome size of P. aeruginosa is approximately 6.3 Mb (Stover et al., 2000); the isolates from cystic fibrosis patients and the environmental strains share more than 80% of this genome sequence (Spencer et al., 2004). The remarkable conservation of genes encoding proteins associated with virulence suggests that most P. aeruginosa strains, regardless of source, possess the same basic pathogenic mechanisms necessary to cause a wide variety of infections.

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1.1.2 Gene Transfer

Horizontal gene transfer has been recognized as one of the major mechanisms driving the evolution of micro-organisms and plays a key role in their ability to adapt to various environments through acquisition of new traits. Studies of several strains of P. aeruginosa, using various hybridization methods or comparison of sequenced genomes, pointed towards the acquisition and exchange of genetic material as an important factor in the genomic diversity and evolution of the species (Kulasekara and Lory, 2004).

The mosaic structure of the P. aeruginosa genome is believed to be the result of multiple acquisitions from different donors during its evolution (Kulasekara and Lory, 2004). Other evidence of horizontal gene transfer includes the presence of genes or remnants of genes associated with mobile elements (i.e., insertion sequences, bacteriophages or plasmids) and the presence of numerous genomic islands (Kulasekara and Lory, 2004), which are horizontally acquired clusters of genes. P. aeruginosagenomic islands have been found to possess genes encoding factors that are involved in genetic mobility and in various virulence traits such as iron uptake functions, antibiotic resistance, biofilm synthesis, type III secretion systems, toxins and adhesins that augment the ability of pathogens to survive in diverse hosts and cause disease (Qui et al., 2009; Kulasekara and Lory, 2004).

The genomes of all P. aeruginosa strains sequenced to date contain a significant fraction of these genomic islands. Different genes carried by a single island often have diverse origins, and blocks are built gradually through insertion and deletion events (He et al., 2004). For example, the well characterized P. aeruginosa genomic island PAPI-1 contains genes that have a high level of similarity with plant pathogens such as Xylella fastidiosa, Agrobacterium tumefaciens, P. syringae and Xanthomonas campestris (Ramos, 2004).

Genetic exchange by conjugation has been observed in clinical and environmental strains of P. aeruginosa (Kidambi et al., 1994; Klockgether et al., 2004; Malloff et al., 2001; Poirel et al., 2004; Yu & Head, 2002), and in freshwater (O’Morchoe et al., 1988). PAPI-1, which encodes a number of virulence factors involved in attachment, biofilm synthesis and antibiotic resistance, was reported to have been transferred by conjugation into recipient P. aeruginosa strains (Qui et al., 2006).

Transduction is another important mechanism of gene transfer for P. aeruginosa. P. aeruginosa bacteriophages were shown to be formidable transducers of naturally occurring microbial communities. For instance, Ripp et al. (1994) reported that phage UT1 is capable of mediating transfer of both chromosomal and plasmid DNA between strains of P. aeruginosa and between P. aeruginosa and indigenous populations of micro-organisms in natural lake water environments.

The impact of gene transfer among P. aeruginosa strains has been demonstrated by their ability to adapt in different niches, their ability to infect a broad range of host organisms, and, most dramatically, by the rapid emergence and dissemination of multiple-antibiotic resistance genes (Blahova et al.,1998; Harrison et al., 2010; He et al., 2004).

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1.1.3 Pathogenicity and Toxicity

The ability of P. aeruginosa to produce infections (pathogenicity) in both human and non-human species is attributed to a wide array of mechanisms, including adherence, invasion, evasion of host defences and damage to host cells (Salyers and Whitt, 2002).

The first step in the pathogenic sequence of P. aeruginosa animal infections is colonization of an epithelial surface using specific adhesins, in order to initiate contact with biological surfaces. Adherence of non-mucoid P. aeruginosato mammalian epithelial cells is mainly mediated by type IV pili which account for 90% of the adherence capacity. In cystic fibrosis patients, P. aeruginosa also binds with mucin which is the main component of the mucus that forms a viscous gel and traps inhaled particles on the airway epithelium (Ramos, 2004).

After the initial step of mammalian colonization, P. aeruginosa produces several extracellular products that can damage tissue and permit dissemination through the bloodstream (toxigenicity). Refer to Appendix 3 for more comprehensive information on these toxins.

Many pathogens, including P. aeruginosa, couple the production of virulence factors with bacterial cell population density to overcome host defences with a consolidated attack. This strategy depends on the ability of an individual bacterial cell to sense other bacterial cells and in response, differentially express specific sets of genes. Such cell-cell communication is called quorum sensing (QS). Production of several of the P. aeruginosa extracellular toxins described in Appendix 3 is coordinated by QS. QS systems in most Gram-negative bacteria function similarly, with an inducer (I) responsible for the biosynthesis of a specific acylated homoserine lactone (HSL) signaling molecule known as the autoinducer. The autoinducer concentration increases with increasing cell density. A receptor (R) binds its cognate autoinducer, forming a complex that activates target gene transcription, thus enabling coordinated expression of genes as a function of cell density. P. aeruginosa employs two dominant QS systems, LasI/LasR and RhlI/RhlR, which function in tandem to control the expression of a number of virulence genes. The LasI/LasR regulates the production of a number of secreted virulence factors responsible for host tissue destruction during the initiation of the infectious process. These include alkaline protease, LasA, LasB and exotoxin A. The LasR/autoinducer complex also activates LasI expression (creating a positive feedback loop) and it activates the second QS system, RhlI/RhlR. The RhlI/RhlR system, in addition to Las A and B, also regulates the production of rhamnolipid and is necessary for optimal production of pyocyanin, cyanide, lipase and alkaline protease (Lazdunski et al., 2004).

Quorum sensing is also important for proper biofilm development. P. aeruginosa readily forms biofilms on biological and abiotic surfaces. Biofilm cells differ from their planktonic counterparts in the genes and proteins that they express, resulting in distinct phenotypes including altered resistance to disinfectants, antibiotics and the human immune system. These cells have been shown to contribute to the persistence of infections and to be up to 1,000 times more resistant to the effects of antimicrobial agents than their planktonic counterparts (Costerton et al., 1999; Mah et al., 2001). Biofilms develop preferentially on inert surfaces, commonly on medical devices and fragments of dead tissue, but they can also form on living tissues (Costerton et al., 1999).

Due to its huge arsenal of metabolic capabilities and ability to exploit many possible nutrients in the environment, P. aeruginosa is often utilized for biodegradation. However, some of the metabolic pathways which allow P. aeruginosa to acquire nutrients, produce compounds, and thrive in the environment have also been linked to its pathogenicity. The ability of P. aeruginosa to obtain nutrients for replication and maintenance is the quintessential factor leading to quorum-sensing-induced virulence expression. Son et al. (2007) identified metabolic pathways which allow P. aeruginosa to degrade amino acids and metabolize lung surfactant lipids as nutrient sources in the lungs of cystic fibrosis patients.

Also involved in P. aeruginosa virulence are signal transduction systems. These are complex signalling systems responsible for eliciting adaptive responses by readily detecting fluctuations in many chemical and physical conditions, which in turn trigger changes in gene expression. P. aeruginosa has an extraordinary number of putative two-component signal transduction systems. It was predicted from the genome sequence analysis that 8.4% of P. aeruginosa genes are involved in regulation. Known two-component regulatory systems in P. aeruginosa have been involved in alginate production, chemotaxis, catabolism of natural substrates, membrane permeability, motility, antibiotic resistance, adhesion, and toxin production (Wang et al., 2003; Richtings et al., 1995; Whitchurch et al., 2004; Yu et al., 1997; Goodman et al., 2004).

Bacteria which cause infection in mammals survive and proliferate most effectively between 20°C and 40°C. The ability of P. aeruginosa to grow optimally at normal body temperature (37°C) also contributes to the extensive incidence of P. aeruginosa infection reported in humans.

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1.1.4 Other Ecological Characteristics

P. aeruginosa is a facultative anaerobe that preferentially obtains its energy via aerobic respiration, but it is well adapted to conditions of limited O2 supply (Palleroni, 1984; Davies et al., 1989).The micro-organism grows optimally at 37ºC and thrives under moist conditions in soil (particularly in association with plants) and in sewage sediments and the aquatic environments (OECD, 1997). It can survive temperatures ranging from 10ºC to 45ºC in both saline and distilled water (Boyle et al., 1991; Garrity 2005; Oberhofer, 1981) and on media pH ranging between 6.0 to 9.0 (Rahman et al., 2005).

P. aeruginosa can use a wide range of organic compounds as a food source, and therefore can adapt to and thrive in many ecological niches including soil, water [river water (Pellett et al., 1983), sea water (Kimata et al., 2004), waste water (Ziegert and Stelzer, 1986)], sediments (Burton et al., 1987), sewage (Havelaar et al., 1985), and oil fields (MacElwee et al., 1990). It has been found to survive in soil and water for periods ranging from 2 to 18 weeks or as long as 4 years if the cells are encapsulated (Ahn et al., 2001; Cassidy et al., 1995; Cassidy et al., 1997; Cornax et al., 1990; Flemming et al., 1994). P. aeruginosa has also been shown to survive in the wheat rhizosphere in the presence of different levels of microbial competition (Morales et al., 1996). It is among the most commonly isolated micro-organisms naturally occurring in petroleum-contaminated soils and groundwater (Ridgway et al., 1990). It is also oligocarbotolerant and can multiply in nutrient-poor environments such as bottled water (Jayasekara et al., 1998; Hunter, 1993). In addition, P. aeruginosa can be found as part of the normal bacterial flora of the intestines, mouth or skin of animals such as cattle, dogs, horses and pigs (OECD, 1997).

Encapsulation and biofilm formation further enhance the ability of the organism to survive in natural and engineered environments (grease traps, water pipes and sewage drain surfaces). The ability of Pseudomonas biofilms to withstand moderate chlorine residuals has lead to the survival of the micro-organism in some water treatment systems (Grobe et al., 2001; Ratnam et al., 1986). According to Teitzel and Parsek (2003), biofilms were observed to be more resistant to heavy metals than planktonic cells in stationary phase or logarithmic growth. The formation of biofilms impedes efforts to control biofouling in a wide variety of industrial settings (Costerton, 2002; Cochran et al., 2000).

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1.2 Effects

1.2.1 Ecological Effects

P. aeruginosa has been described as an opportunistic pathogen of plants (Bradbury, 1986) and is recognized as a Risk Group 2 pathogen by the Canadian Food Inspection Agency (Animal Pathogen Import Program). Generally, a Risk Group 2 pathogen is any pathogen that can cause disease but, under normal circumstances, is unlikely to be a serious hazard to healthy organisms in the environment. If needed, effective treatment and preventive measures are available, and the risk of spread is limited. A number of pathogenicity/toxicity studies used P. aeruginosa (or its isolated toxins) in a variety of hosts, including plants, invertebrates and vertebrates (Appendix 4, 5A and 5B). A literature search revealed two cases where P. aeruginosa was identified as the causative agent in a naturally-occurring infection in an agricultural setting (Appendix 5B). P. aeruginosa was isolated from infections in four other veterinary cases, but was not definitively shown to be the causative agent. In susceptible plants, P. aeruginosacauses a soft rot that can kill the host; in infected mammals, symptoms can range widely including sepsis, inflammation and pneumonia depending on the site of infection. If the site is a critical body organ such as the lungs or kidneys, the results can be fatal. Many studies have verified that P. aeruginosacan behave as an opportunistic pathogen in a range of plants, invertebrates and vertebrates, for example, when the host has been stressed or weakened by another factor. However, in the absence of such stressors or factors, infection will not occur. In addition, there was no evidence in the scientific literature to suggest any adverse ecological effects at the population level.

As shown in Appendix 5A, results of pathogenicity and chronic toxicity testing with these strains towards the following terrestrial invertebrates: Folsomia candida (P. aeruginosa 31480, 700370, and 700371), Folsomia fimetara (P. aeruginosa 31480, 700370, and 700371) and Eisenia andrei (P. aeruginosa 31480), demonstrated no adverse effect on adult mortality or juvenile reproduction of these springtails and earthworm species (Princz, 2010). Definitive plant testing using barley (Hordeum vulgare with P. aeruginosa 700370), red fescue (Festuca rubra with P. aeruginosa 31480), red clover (Trifolium pratense with P. aeruginosa31480 and 700371) and northern wheatgrass (Elymus lanceolatus with P. aeruginosa 700371) demonstrated no adverse effect on seedling emergence, shoot and root length and dry mass (Princz, 2010) when tested according to the “Guidance Document for Testing the Pathogenicity and Toxicity of New Microbial Substances to Aquatic and Terrestrial Organisms (EPS 1/RM/44, March 2004)”, developed by Environment Canada.

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1.2.2 Effects on Human Health

There is little evidence to demonstrate that environmental P. aeruginosa isolates differ in pathogenicity from clinical isolates, and as indicated in Section 1.1.1, there are studies which show that some P. aeruginosa environmental isolates are indistinguishable from clinical strains, and that many clinical strains are also isolated from the environment. Therefore, in the absence of strain-specific evidence, surrogate information used to characterize the potential human health hazard from the DSL-listed P. aeruginosa strains will include environmental isolates.

Extensive literature searches show that P. aeruginosais essentially an opportunistic pathogen. As such, to initiate infection, P. aeruginosa usually requires a substantial break in first-line defences. Such a break can result from breach or bypass of cutaneous or mucosal barriers (e.g., trauma, surgery, serious burns, indwelling devices, mucosal clearance defects from cystic fibrosis), disruption of the protective balance of normal mucosal flora by broad­spectrum antibiotics, or alteration of the immunologic defence mechanisms (e.g., in chemotherapy-induced neutropenia or AIDS), and co-morbidity (diabetes mellitus, heart disease, etc.). P. aeruginosa is associated with numerous chronic and progressive respiratory diseases. It is responsible for life-threatening nosocomial infections and infections in immunocompromised individuals. It has also been implicated in localized and systemic infections in otherwise healthy individuals. Numerous P. aeruginosa outbreaks have been reported worldwide (Appendix 6).

Respiratory infections caused by P. aeruginosa occur almost exclusively in individuals with a compromised respiratory tract. It has been reported as the causative pathogen in mechanically ventilated patients (Brewer et al., 1996; Dunn & Wunderink, 1995, Nag et al., 2005), and acute and chronic sinusitis (Bert & Lambert-Zechovcky, 1996; Danielides et al., 2002; Farr & Ramadan, 1993; Koltai et al., 1985; O’Donnell et al., 1993; Suzuki et al., 1996; Guss et al., 2009). P. aeruginosa is the leading cause of morbidity and mortality in children and adults with Cystic Fibrosis (CF) (Govan & Deretic, 1996; Moss, 1995; Pier, 2000; Speert, 2002; Yu & Head, 2002). CF is a disease caused by an inherited genetic defect. According to the Canadian Cystic Fibrosis Foundation, approximately 3,500 children, adolescents, and adults with cystic fibrosis attend specialized CF clinics. CF leads to changes in the bronchial mucosa that normally prevents microbial infection (Pier, 2000). These changes limit physio-chemical mechanisms that remove excess mucus and debris (e.g., cellular debris, microbes, etc.) from the airways (Govan and Deretic, 1996), permitting repeated microbial colonization of the major airways and pulmonary infections. Most CF patients are ultimately infected with P. aeruginosa. In 2002 it was reported that by the time CF patients reach adulthood, approximately 80% are chronically infected with P. aeruginosa (Speert, 2002), which takes advantage of the highly compartmentalized and anatomically deteriorating lung environment and resists the challenges of the immune defence and antibiotic therapy (Oliver et al., 2000). Recent studies have shown that early aggressive eradication therapy with colistin and ciprofloxacin for intermittent P. aeruginosa airway colonization in cystic fibrosis patients postpones the next occurrence of P. aeruginosa compared to no treatment, and protects up to 80% of patients from development of chronic infection for up to 15 years (Hansel et al., 2008).

Chronic airway infections with P. aeruginosa are regularly seen in patients with advanced stages of chronic obstructive pulmonary disease (COPD). About 15% of the population in North America and Europe are affected by COPD. Intermittent colonization with P. aeruginosa is observed in about 30% of patients with COPD. Chronic airway infections with P. aeruginosa with substantial morbidity and mortality emerge in 5% of COPD patients (Murphy, 2009).

P. aeruginosa also has the ability to cause life-threatening community-acquired or nosocomial infections. The micro-organism is the third leading cause of hospital-acquired urinary tract infections, accounting for about 12 percent of all infections of this type (Pollack, 1995; Shigemura et al., 2009). These infections are commonly related to urinary tract catheterization, instrumentation or surgery. Endocarditis due to P. aeruginosa has been seen in patients with prosthetic heart valves (Wieland, 1986; Kato et al., 2009). In rare cases, it has been associated with meningitis or brain abscess (Pollack, 1992; Huang et al., 2007). P. aeruginosa accounts for 8% of wound infections, including burns (Kluytmans, 1997). According to Kluytmans (1997), in burn patients P. aeruginosa bacteremia has declined as a result of better wound treatment and removal of raw vegetables, which can be contaminated with P. aeruginosa, from the diet. However, P. aeruginosa outbreaks in burn units are associated with high (60%) death rates (Richard et al., 1994). P. aeruginosa is a frequent isolate from wounds, particularly those contaminated with soil, plant material or water. Puncture wounds, particularly those penetrating the bone, may result in osteomyelitis or osteochondritis. The former is common in intravenous drug abusers (Arstenstein & Cross, 1993) and the latter in puncture wounds to the feet in children and diabetics (Jarvis & Skipper, 1994; Lavery et al., 1994; Pollack, 1992; Hartemann-Heurtier & Senneville, 2008).

In individuals with severe immunodeficiencies, such as AIDS, cancer, and bone marrow transplant patients, P. aeruginosaappears to be the major cause of bacteremia (Mendelsen et al., 1994; Manfredi et al., 2000; Saghir et al., 2009). Patients being treated for cancer and people living with AIDSare also at greater risk of acquiring P. aeruginosapneumonia (Krcmery et al., 2006).

P. aeruginosa has also been associated with a variety of localized skin, ear and eye infections in otherwise healthy individuals (Hatchette et al., 2000; Hendersen et al., 1992, Huang et al., 2002; Parkin et al., 1997; Viola et al., 2006). Moisture is a common factor in these infections and consequently infection occurs primarily in moist areas such as the ear, the toe webs, the perineal region, under the diapers of infants, and the skin of whirlpool and hot tub users. Otorhinolaryngologic infections due to P. aeruginosa range from superficial and self-limiting to life-threatening. The most serious ear infection due to this organism is malignant otitis externa, usually resulting from a failure of topical therapy, and resulting in an invasive disease destroying tissue which may progress to osteomyelitis at the base of the skull and possible cranial nerve abnormalities (Arstenstein & Cross, 1993). Other ear infections associated with P. aeruginosa include external otitis, otitis media, chronic suppurative otitis media, and mastoiditis (Arstenstein & Cross, 1993; Kenna, 1994; Legent et al., 1994; Pollack, 1992). P. aeruginosa has also been implicated in folliculitis and unmanageable forms of acne vulgaris. Eye infections attributed to P. aeruginosa are frequently associated with contact lens use. Contaminated contact lens solution and the use of tap water during lens care have been implicated as a source of P. aeruginosa infection (Holland et al., 1993).

All micro-organisms are considered to be potential sensitizers, though to date, no P. aeruginosa isolates have been described as allergens. As do all Gram negative bacteria, Pseudomonads possess endotoxin (i.e., lipopolysaccharides), which may cause an innate febrile immune response on exposure (Schroeder et al., 2002).

Treatment of human infection with P. aeruginosa is hampered by its ability to readily acquire resistance to antimicrobial drugs. Extensive use of antibiotics to treat P. aeruginosa, particularly in CF patients, has exerted the selective pressure to encourage resistance development. P. aeruginosa displays high­level multiple intrinsic resistance to a variety of structurally unrelated and clinically important antimicrobial agents, which greatly complicates the clinical management of infected patients. These include ampicillin, amoxicillin-clavulanic acid, ampicillin-sulbactam, tetracyclines, macrolides, rifampin, chloramphenicol, trimethoprim/sulfamethoxazole, narrow- and extended-spectrum cephalosporins, and oral-broad spectrum cephalosporins (cefixime and cefpodoxime) (Kiska & Gilligan, 1999). Table 3 represents an antibiogram generated by Health Canada for the characterization of DSL-listed P. aeruginosa strains.

Table 3: Minimal Inhibitory Concentration (MIC)[1] for the DSL-listed P. aeruginosastrains

AntibioticATCC 31480ATCC 700370ATCC 700371
Amphotericin B>24>24>24
Aztreonam16 ± 6.96 ± 00.9 ±0.6
Doxcycline16 ±6.96 ± 00.37 ± 0
Gentamicin1 ± 0.41 ± 0.40.6 ±0.2
Nalidixic acid>24>243.5 ±2.3
Trimethoprim>24>2410 ±3.5
[1] Work conducted using TSB-MTT liquid assay method to characterize the P. aeruginosa DSL strains (Seligy et al, 1997). The reported values are based on a minimum of 3 independent experiments. Values correspond to the minimal inhibitory concentration (ug/ml) for select P .aeruginosastrains (20, 000 CFU/well) grown in the presence of antibiotic for 24 hrs at 37°C.

MICtests performed by Milne and Gould (2009) on 315 multidrug resistant P. aeruginosa cystic fibrosis isolates and their clinical interpretation are shown in Table 4. Overall, 32.1% of the isolate/drug combinations were susceptible and 49.5% were resistant.

Table 4: P. aeruginosa MIC results on clinically relevant antibiotics

 AntibioticEtest range MIC (mg/L)SusceptibleIntermediateResistant
low (mg/L)high (mg/L)Number testedrangeMIC50MIC90number%number%number%
Collistin0.01610243150.094 to >10240.75626684289217
Amikacin0.0162563151.5 to >25648>2569932732314345
Ciprofloxacin0.002323150.064 to >32289530143457725
Meropenem0.002323150.023 to >3224>328828401318759
Piperacillin0.0162561340.75 to >256>256>2563627009873
Piperacillin/ Tazobactam0.0162563130.38 to >256>256>25684274122572
Netilmicin0.0162562730.38 to >256161286825993610639
Aztreonam0.0162563150.04 to >256>256>256762425821468
Ceftazidime0.0162563130.125 to >256>256>256692223722171
Levofloxacin0.002323150.19 to >326>3267211123613643
Gentamicin0.06410243140.5 to >256124865211223912740
0.0162563060.19 to >256>256>25663216223777
Imipenem0.002323150.19 to >32>32>32451411425982
Adapted from Milne and Gould (2009)

To assess the effectiveness of these antibiotics compared to previous years, Milne and Gould (2009) plotted the annual geometric mean MIC values for the individual antimicrobials (Figure 1). The only two antibiotics to demonstrate a downward trend were levofloxacin and colistin. The trend for ciprofloxacin was level. There was an upward trend in the aminoglycoside MICs, which was least in gentamicin and greatest in tobramycin. Tobramycin susceptibility showed a steady drop from 86% to 54.8% between 2001 and 2006 (data not shown), with an increase in intermediate susceptibility from 6% in 2001 to 33.3% in 2006. With the exception of piperacillin, all other antimicrobials show minor annual fluctuations in susceptibility patterns.

Figure 1. Annual Geometric Means of the Aminoglycoside MICs. AMK : Amikacin (R2 = 0,5228) – GEN, Gentamicin (R2 = 0,2908) – NET, Netilmicin (R2 = 0,0598) – TOB, Tobramycin (R2 = 0,9362)

Figure 1: Annual geometric means of the aminoglycoside MICs. AMK, amikacin; GEN, gentamicin; NET, netilmicin; TOB, tobramycin

Also, a total of 1663 combination tests were performed on 44 different antimicrobial pairs. As can be seen in Table 5, synergy was most frequently found with β-lactam and quinolone combinations (10%), followed by β-lactam and aminoglycoside combinations (5%) and carbapenem and quinolone combinations (4%). Antagonism was only found with a β-lactam and quinolone combination (1%).

Table 5: Summary of extended susceptibility testing on 315 strains of P. aeruginosa

First antimicrobial groupSecond antimicrobial group
Aminoglycosiden = 1217
(37% S, 32% R)
n = 443n = 260n = 58n = 117
β-lactamSYN = 5%
ANT = 0%
n = 1381
(24% S, 72% R)
n = 443n = 149n = 209
CarbapenemSYN = 1%
ANT = 0%
Not applicablen = 630
(21% S, 71% R)
n = 144n = 140
ColistinSYN = 0%
ANT = 0%
SYN = 3%
ANT = 0%
SYN = 1%
ANT = 0%
n = 315
(84% S, 7% R)
n = 143
QuinoloneSYN = 1%
ANT = 0%
SYN = 10%
ANT = 1%
SYN = 4%
ANT = 0%
SYN = 2%
ANT = 0%
n = 630
(26% S, 34% R)
Adapted from Milne and Gould (2009)
S, susceptible; R, resistant; SYN, synergy; ANT, antagonism.

Cells highlighted grey, number of MICs (% susceptible, % resistant); data to right of highlighted cells, number of times combination tested; data to left of highlighted cells, combination results.

In Canada, the most active agents against P. aeruginosaisolates from intensive care units between 2005 to 2006 were amikacin, cefepime, meropenem, and piperacillin/ tazobactam with MIC90(μg/mL) of 16, 32, 16, and 64, respectively (Zhanel et al., 2008). Aggressive antibiotic treatment at early onset of P. aeruginosa infection in CF patients has been shown to be promising (Hansen et al., 2008), while the use of combination antibiotic treatments to enhance antibacterial efficacy are continuously being investigated (Louie et al., 2010).

The ability of the P. aeruginosa DSL strains to grow optimally at 37°C, as shown in Appendix 1A, is a concern from a human health standpoint. In vivo tests were conducted at Health Canada to evaluate the potential of the 3 DSL-listed P. aeruginosa strains to cause adverse immune effects. Results, as shown in Appendix 5A, indicate that P. aeruginosastrains ATCC 31480, ATCC 700370 and ATCC 700371 induced some transient immune-related effects in BALB/c mice 2 and 4 hours after inhalation.

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1.3 Hazard Severity

The environmental hazard severity for P. aeruginosa ATCC 31480, 700370 and 700371 is estimated to be medium[1]. Information from the scientific literature indicates that P. aeruginosa is an opportunistic pathogen. Such pathogens, under certain conditions that pre-dispose the host to infection cause a range of symptoms that will debilitate the host and could kill it. However, in the absence of such conditions, infection will not occur. This is consistent with the observation that there is no evidence in the scientific literature to suggest any adverse ecological effects at the population level.

As mentioned previously, specific research results using the DSL-listed strains demonstrated no adverse effect on adult mortality or juvenile reproduction of springtails (Folsomia spp.) and earthworm (Eisenia andrei) species nor any adverse effect on barley (Hordeum vulgare), red fescue (Festuca rubra), red clover (Trifoliumpratense) and northern wheatgrass (Elymus lanceolatus).

The human hazard severity for P. aeruginosa ATCC 31480, 700370 and 700371 is estimated to be medium (see appendix 7). Information from the scientific literature indicates that this micro-organism has pathogenic potential in both otherwise healthy and immunocompromised humans. P. aeruginosa is recognized by the Public Health Agency of Canada as a Risk Group 2 human pathogen and has the ability to spread and acquire clinically relevant antibiotic resistance genes. P. aeruginosaproduces a wide variety of extracellular enzymes and toxins that are important factors for its pathogenicity in susceptible humans.

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2. Exposure Assessment

An exposure assessment identifies the mechanisms by which a micro-organism is introduced into a receiving environment (Section 2.1) and qualitatively and/or quantitatively estimates the magnitude, likelihood, frequency, duration, and/or extent of human and environmental exposure (Section 2.2). The exposure to the micro-organism itself, its genetic material or its toxins, metabolites or structural components is assessed.

2.1 Sources of Exposure

Pseudomonas aeruginosa, as a species, is generally considered a ubiquitous bacterium, occurring naturally in many moist environmental media; it has the ability to adapt to and thrive in many ecological niches. However, this ‘background’ level presence of P. aeruginosa has not been well characterized, and, while acknowledged as a potential source of natural exposure, is not the focus of this screening assessment. With respect to the specific strains that are the focus of this assessment, to date, no quantitative studies were found on their background levels in the Canadian environment. P. aeruginosa as a species has properties that make it of commercial interest in a variety of industries. A search of the public domain (internet, patent databases) suggests multiple potential uses, including waste degradation, particularly in oil refineries, and in textile, pulp and paper, mining and explosives industries, as well as in commercial and household drain cleaners and degreasers, septic tank additives and general cleaning and odour-control products.

The three strains of P. aeruginosa listed on the DSL were imported into Canada between 1984 and 1986 to be used in a variety of waste, water and wastewater treatments, bioremediation, and biodegradation products. The government has attempted to verify continued commercial or consumer activity with these strains. No uses were identified in 2007 based on the outcome of a voluntary questionnaire sent to a subset of key biotechnology companies and on information obtained from other federal government regulatory and non-regulatory programs.

In 2009-2010, the government conducted a mandatory information-gathering Notice (survey) under section 71 of CEPA as published in the Canada Gazette on October 3rd, 2009. The Notice applied to any persons who, during the 2008 calendar year, manufactured or imported a DSL substance, whether alone, in a mixture, or in a product. Anyone meeting these reporting requirements was legally obligated to respond. Respondents were required to submit information on the industrial sector, uses and any trade names associated with products containing these strains, as well as the quantity and concentration of the strain imported or manufactured in the 2008 calendar year. No commercial or consumer activities using P. aeruginosa ATCC 31480, ATCC 700370 or ATCC 700371 were reported in response to the section 71 Notice. For the purposes of this exposure assessment, it is assumed that these strains are no longer imported or manufactured in Canada for commercial or consumer uses, based on the absence of responses to this survey.

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2.2 Exposure Characterization

2.2.1 Environment

Persistence data was obtained by Environment Canada on ATCC 31480, 700370 and 700371; it shows that strain-specific DNA could be amplified from agricultural soil 62, 122 and 126 days, respectively, after live cells were introduced (Xiang et al., 2010). However, there was no attempt to recover live cells from the soil, so specific strain survivability of the three P. aeruginosa strains in the soil was not demonstrated (see Appendix 5A). ATCC 31480 showed no growth in 10 days at 14°C on nutrient broth and nutrient agar (Spraker, 1982). However, given the ubiquity of the species, one could assume that these strains are also able to survive for considerable lengths of time in soil and other media even if there is no evidence of proliferation.

The most likely routes of introduction of the three DSL-listed P. aeruginosa strains into the environment due to household, industrial or manufacturing activities would be into water and soil. The magnitude of exposure (including geographic distribution, timing, duration and frequency of exposure) is presumed to be proportional with the amount of bacteria released into the environment according to the use.

While large inputs of DSL strains into the environment could likely result in concentrations greater than background levels, high numbers are unlikely to be maintained in water and in soil due to natural competition (Leung et al., 1995) and microbiostasis (van Veen et al.,1997), which is an inhibitory effect of soil that results in the rapid decline of populations of introduced bacteria. This is consistent with the research results noted above.

No relevant reports concerning persistence in the environment of toxins produced by P. aeruginosa have been found.

The environmental exposure for P. aeruginosa ATCC 31480, 700371, and 700370 is estimated to be low[2] from consumer and industrial activities or from other anthropogenic sources. This estimation is supported by evidence that these strains were no longer imported, manufactured or used in Canada in 2008, as found through responses to the mandatory section 71 Notice and by results from the voluntary survey conducted in 2007.

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2.2.2 Humans

P. aeruginosa is considered a Risk Group 2 pathogen requiring a Level 2 containment under the Public Health Agency of Canada’s Laboratory Biosafety Guidelines (3rd Ed. 2004). P. aeruginosa can be transmitted through direct contact with contaminated water or aerosols (Reuter et al., 2002; Moore et al., 2004; Saiman and Siege, 2003). Other modes of transmission include contact of susceptible individuals with discharge from conjunctivae (Lyzak et al., 2000) or the upper respiratory tract (Moore et al., 2004; Saiman and Siege, 2003) of infected persons and through contact with contaminated surfaces, such as sinks, tap water outlets, cleaning equipment, flower vases and humidifiers (Ayliffe et al., 1974; Reuter et al., 2002; Grieble et al., 1970; Taplin and Mertz, 1973; Engelhart et al., 2002), improperly sterilized medical equipment (De Vos et al., 1997; Elhag et al., 1977; Muyldermans et al., 1998), and contaminated distilled water, IV fluids, and antiseptics (Favero et al., 1971; Parrott et al., 1982).

As previously mentioned, P. aeruginosa is commonly found in the environment. The purpose of this section is to characterize the human exposure to the 3 DSL-listed P. aeruginosa strains from their deliberate addition to consumer or industrial products used in Canada.

Humans are likely to be exposed to P. aeruginosathrough inhalation or dermal contact as the micro-organisms are dispersed in the atmosphere attached to dust particles or aerosolized during manufacturing and product application. P. aeruginosa is strongly associated with respiratory infections. Therefore, the most problematic route of exposure to products containing P. aeruginosa is considered to be from inhaling aerosols, whether the product is in liquid or powder formulation. Dermal exposure may also affect humans. Since skin is a natural barrier to microbial invasion of the human body, infection would be more likely to occur if the skin was damaged through abrasions and burns.

The human exposure estimation for P. aeruginosa ATCC 31480, 700370 and 700371 is low[2], notwithstanding (i) the organism’s ability to cause persistent infections from which it could be shed, (ii) the organism’s ability to persist and establish itself in diverse environments, including manmade environments such as drains, (iii) the organism’s inherent resistance to disinfectants and antibiotics; and based on evidence that these strains are no longer imported, manufactured or used in Canada, as found through the mandatory section 71 Notice for the 2008 calendar year.

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3. Risk Characterisation

Based on the medium level of hazard of the three strains of P. aeruginosa listed on the DSL to human health and, uniquely, also to other biota in the Canadian environment and the likely low potential for exposure as assessed by the absence of reported uses through the section 71 survey for the 2008 calendar year, the risk is estimated to be low[3] with respect to the environment and medium with respect to human health.

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Based on available information, it is proposed that P. aeruginosa strains ATCC 31480, ATCC 700370 and ATCC 700371 are not entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity or that constitute or may constitute a danger to the environment on which life depends. Therefore, it is proposed that these strains do not meet the definition of toxic as set out in section 64 of the CEPA1999.

Given the hazardous properties and the current low likelihood of exposure to these strains in Canada, new activities (i.e., importation into, manufacture or use within Canada) for these strains which have not been identified or assessed under CEPA 1999 could increase the potential for exposure and may lead to these strains meeting the criteria set out in section 64 of the Act. Therefore, it is recommended that these substances be subject to the Significant New Activity (SNAc) provisions specified under subsection 106(3) of the Act, to ensure that any new import, manufacture or use of the substance is notified under the New Substances Notification Regulations (Organisms) and will undergo appropriate environmental and human health risk assessments as specified in section 108 of the Act prior to the substance being re-introduced into Canada.

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Viola, L., A. Langer, S. Pulitanò, A. Chiaretti, M. Piastra, and G. Polidori. 2006. Serious Pseudomonas aeruginosainfection in healthy children: case report and review of the literature. Pediatrics International. 48(3): 330-333.

Vives-Flórez, M., and D. Garnica. 2006. Comparison of virulence between clinical and environmental Pseudomonas aeruginosaisolates. Internat Microbiol.9:247-252.

Walker, S.E., J.E. Sander, J.L. Cline and J.S. Helton. 2002. Characterization of Pseudomonas aeruginosa Isolates associated with mortality in broiler chicks. Avian Diseases. 46:1045-1050.

Walker, T.S., H.P. Bais, E. Déziel, H.P. Schweizer, L.G. Rahme, R. Fall, and J.M. Vivanco. 2004. Pseudomonas aeruginosa-plant root interactions. Pathogenicity, biofilm formation, and root exudation. Plant Physiol.134:320-331.

Wang Y, Ha U, Zeng L, Jin S. 2003. Regulation of membrane permeability by a two-component regulatory system in Pseudomonas aeruginosa. Antimicrob Agents Chemother. 47:95-101

Wieland, M., M.M. Lederman, C. Kline-King, T.F. Keys, P.I. Lerner, S.N. Bass, R. Chmielewski, V.D. Banks, and J.J. Ellner 1986. Left-sided endocarditis due to Pseudomonas aeruginosa. A report of 10 cases and review of the literature. Medicine (Baltimore). 65(3):180-9.

Wilderman PJ, Vasil AI, Johnson Z, Wilson MJ, Cunliffe HE, Lamont IL, Vasil ML. 2001. Characterization of an endoprotease (PrpL) encoded by a PvdS-regulated gene in Pseudomonas aeruginosa. Infect Immun. 69(9):5385-94.

Wolfgang MC, Kulasekara BR, Liang X, Boyd D, Wu K, Yang Q, Miyada CG, Lory S. 2003. Conservation of genome content and virulence determinants among clinical and environmental isolates of Pseudomonas aeruginosa. Proc Natl Acad Sci USA. 100(14):8484-9.

Wyman, M., Swanson, C., Kowalski, J.J., Powers, J.D. and Boraski, E.A. 1983. Experimental Pseudomonas aeruginosaulcerative keratitis model in the dog. American Journal of Veterinary Research. 44(6):1135-1140.

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Yu H, Mudd M, Boucher JC, Schurr MJ, Deretic V. 1997. Identification of the algZ gene upstream of the response regulator algR and its participation in control of alginate production in Pseudomonas aeruginosa. J Bacteriol. 179(1):187-93.

Zhanel GG, DeCorby M, Nichol KA, Wierzbowski A, Baudry PJ, Karlowsky JA, Lagacé-Wiens P, Walkty A, Mulvey MR, Hoban DJ, and Canadian Antimicrobial Resistance Alliance. 2008. Antimicrobial susceptibility of 3931 organisms isolated from intensive care units in Canada: Canadian National Intensive Care Unit Study, 2005/2006.Diagn Microbiol Infect Dis. 62(1):67-80.

Ziegert, E., and W. Stelzer. 1986. Comparative study of the detection of Pseudomonas aeruginosa in water [Vergleichende Untersuchungen zum Nachweis von Pseudomonas aeruginosa im Wasser.] Zentralblatt fur Mikrobiologie. 141(2):121-128.

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Appendix 1A: Characteristics of DSL-listed P. aeruginosa strains – Growth Rate in Trypticase Soy Broth[*]

Characteristics of DSL-listed P. Aeruginosa Strains – Growth Rate in Trypticase Soy Broth. The graphs show changes in optical density (OD) of DSL P. aeruginosa strains (P. aeruginosa strains 31480, 700370 et 700371) grown at various temperatures in Trypticase Soy Broth (TSB) (TSB of 28C, 32C, 37C and 42C). At time 0, bacteria were at 106 cfu/well. Kinetic measurements were taken every 15 min with a multi-well spectrophometer at a wavelength of 500 nm.

The graphs show changes in optical density (OD) of DSL P. aeruginosa strains grown at various temperatures in Trypticase Soy Broth (TSB). At time 0, bacteria were at 106cfu/well. Kinetic measurements were taken every 15 min with a multi-well spectrophometer at a wavelength of 500 nm.

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Appendix 1B: Characteristics of DSL-listed P. aeruginosa strains - Growth on Different Media at 28°C and 37°C (48 hours)[*]

 StrainsTSB (1)5% Sheep
Starch (2)Mac-Conkey
Agar (3)
Lysin Iron (4)Triple Sugar Iron - with pheol red

Red - neutral to alkaline

Yellow -acidic (5)
Urea (6)MYP supple-ments (7)Man-nitol (8)Citrate

Green-neutral to acidic

Blue-alkaline (9)
Catalase Activity in TSB (10)
Bacteria28 C37C28C37Cgrowth 37 CHydrolysis 37 C28 C37 C28 C37 C28 C37 C28 C37 C28 C37 C28 C37 C28 C37 C28 C37 C
P. aeruginosa 31480++ Green diffusing pigment-+ Green colony pigment++++-------+
P.aeruginosa 700370+■ / ◙-++----++/-++
P. aeruginosa 700371++■ / ◙+-+++++------+weak
 Colonies are black when illuminated with UV 365nm
☼ fluorescent colonies when illuminated with UV365nm
■ no clearing or discolouration observed
◙ discolouration or clearing localized to site of colony
(1) all purpose medium
(2) differential medium that tests the ability of an organism to produce extracellular enzymes that hydrolyse starch
(3) detection of coliform organisms in milk and water; tests for ability of organism to ferment lactose
(4) simultaneous detection of lysine decarboxylase and formation of hydrogen sulfide in the identification of Enterobacteriaceae, in particular Salmonella and Arizona according to Edwards and Fife.
(5) gram-negative enteric bacilli based on glucose, lactose, and sucrose fermentation and hydrogen sulfide production
(6) screening of enteric pathogens from stool specimens - Urea metabolism
(7) B.cereus selective agar
(8) isolation and differentiation of Staphylococci
(9) Citrate utilization test, ability to use citrate as the sole carbon source.
(10) Catalase enzyme assay measures anti-oxidant activity (hydrogen peroxide to water and oxygen).

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Appendix 1C: Characteristics of DSL-listed P. aeruginosa strains – Fatty Acid Methyl Ester (FAME) Analysis[*]

Data presented shows the best match between the sample and different MIDI@ databases (clinical and environmental), along with the number of matches (fraction of total number of tests) and the fatty acid profile similarity index (in parentheses; average of all matches).

Test StrainEnvironmental DatabaseClinical DatabaseBioterrorism Database
P. aeruginosa ATCC 314808/9 P. aeruginosa (0.898)
1/9 E. cloacae (0.876)
8/8 P. aeruginosa (0.725)No match
P. aeruginosa ATCC 70037011/11 P. aeruginosa (0.880)5/6 P. aeruginosa (0.766) 1/6 No matchNo match
P. aeruginosa ATCC 7003717/7 P. aeruginosa (0.722)8/8 P. aeruginosa (0.886)No match
MIDI@ is a commercial identification system that is based on the gas chromatographic analysis of cellular fatty acid methyl esters.

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Appendix 2: List of some Pseudomonas aeruginosa mobile elements and associated traits

TypeNamePathogenic traitsReferences
Plasmid  pMG1Resistance to borate, gentamycin, mercury, streptomycin, sulphonamide, tellurite, ultraviolet lightJacoby, 1974
R151Resistance to carbenicillin, gentamycin, kanamycin, streptomycin, sulphonamide, tobramycinBryan et al., 1974
Rms 149Resistance to carbenicillin, gentamycin, streptomycin, sulphonamideHedges & Jacoby, 1980
Integron In4Resistance to gentamycin, streptomycin, carbenicillinPartridge et al., 2001
In28Resistance to carbenicillin, streptomycin, spectinomycin, and chloramphenicolPartridge et al., 2001
Transposon  Tn501Resistance to mercuryStanisich et al., 1989
Tn1696Resistance to mercury, sulphonamide
Integron In4
Partridge et al., 2001
Tn1403Integron In28Partridge et al., 2002

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Appendix 3: List of toxins produced by P. aeruginosa

Exotoxin A
  • activity is similar to the cytotoxic activity of the diphtheria toxin
  • catalyzes ADP­ribosylation and the inactivation of elongation factor 2 (EF-2), leading to inhibition of protein biosynthesis and cell death.
  • Exotoxin A is responsible for local tissue damage, bacterial invasion, and (possibly) immunosuppression.
Collier, 1975; Salyers & Whitt, 2002; Vidal et al., 1993
Exoenzyme S (ExoS)
  • Type III-secreted cytotoxin which is an ADP­ribosyl transferase, but unlike exotoxin A, it does not modify EF-2 and it preferentially ribosylates GTP­binding proteins.
  • production of ExoS is associated with the ability of P. aeruginosa to spread or disseminate from epithelial colonization sites to the bloodstream of infected individuals, resulting in the development of a fatal sepsis.
Nicas & Iglewski, 1985; Salyers & Whitt, 2002
Exoenzyme T (ExoT)
  • Type III-secreted cytotoxin which is an ADP­ribosyl transferase, but has only 0.2% of the catalytic activity of ExoS.
  • inhibits bacterial internalization by eukaryotic cells. ExoT ADP-ribosylates specifically the Crk-I and CrkII adaptor proteins, which are part of signalling pathways involved in focal adhesion and phagocytosis
Sun & Barbieri, 2003
Exoenzyme U (ExoU)
  • Type III-secreted cytotoxin which induces damage to internal and plasma membranes leading to membrane permeability and cell lysis.
  • mediates killing of a variety of mammalian cell types in vitro, including macrophages, epithelial cells and fibroblasts.
  • intoxication with ExoU is associated with lung injury, bacterial dissemination and sepsis in animal model and human infections.
Sato et al., 2003
Exoenzyme Y (ExoY)
  • Type III-secreted cytotoxin that is an adenylate cyclase that elevates the intracellular cAMP levels in eukaryotic cells and causes rounding of certain cell types.
Feltman et al., 2001
Haemolytic Phospolipase C (PlcH)
  • virulence determinant of P. aeruginosa in a variety of infections in mammals, plants, yeast, and insects.
  • critical component in the pathogenesis of P. aeruginosa primarily in pulmonary infections
Barker et al., 2004; Chin & Watts, 1988; Hogan & Kolter, 2002; Hollsing et al., 1987; Jander et al., 2000; Ostroff et al., 1989; Rahme et al., 1995; Vasil et al., 2009
  • a rhamnose­containing glycolipid biosurfactant believed to solubilize the phospholipids of lung surfactant, making them more accessible to cleavage by phospholipase C.
  • resulting loss of lung surfactant may be responsible for the atelectasis associated with chronic and acute P. aeruginosa lung infection.
  • inhibits the mucociliary transport and ciliary function of human respiratory epithelium.
Read et al., 1992; Van Gennip et al., 2009; Alhede et al., 2009
LasB elastase, LasA elastase
  • responsible for elastolytic activity. Elastolytic activity is believed to destroy elastin­ containing human lung tissue and cause the pulmonary haemorrhages of invasive P. aeruginosainfections.
  • LasB elastase and LasA elastase cleave collagen, IgG and IgA.
  • lyse fibronectin to expose receptors for bacterial attachment on the mucosa of the lung.
Parmely, 2000; Salyers & Whitt, 2002
  • secondary metabolite shown to alter the pro-inflammatory/anti-inflammatory balance within the human airway epithelial cells and thus contributes to the pathogenicity of Pseudomonas -associated lung disease.
  • interferes with the regulation of ion transport, ciliary beat frequency, and mucus secretion in airway epithelial cells by altering the cytosolic concentration of calcium
  • inhibits cytotoxic T-cell proliferation by decreasing the production of the critical lymphokine interleukin 2 (IL-2) and the expression of the IL-2 receptors on the T cell membrane.
Denning et al., 1998a; Denning et al., 1998b; Caldwell et al., 2009; Kong et al., 2006; Lau et al., 2004
Phenazine-1-carboxylic acid
  • secondary metabolite which affects human airway epithelial cells by several mechanisms, including increasing IL-8 release and ICAM-1 (intracellular adhesion molecule-1) expression, increasing intracellular oxidant formation, as well as decreasing RANTES (Regulated on Activation, Normal T Expressed and Secreted) and MCP-1 (monocyte chemotactic protein-1) release.
Denning et al., 2003
  • causes immediate slowing of ciliary beat frequency on contact thus disrupting the pattern of ciliary beating. This effect is correlated closely with delay in mucociliary clearance. Such delay would advantage bacteria by giving them time to multiply and produce virulence factors in sufficient quantities to establish an infection.
Dowling & Wilson, 1998; Munro et al., 1989
Hydrogen cyanide
  • produced by clinical isolates of P. aeruginosa from CF patients at low oxygen tension and high cell densities during the transition from exponential to stationary growth phase.
  • a potent inhibitor of cellular respiration, is produced under microaerophilic growth conditions at high cell densities.
  • cyanide levels are associated with impaired lung function.
Castric, 1983; Pessi & Haas, 2000; Ryall et al., 2008
Pyoverdine and pyochelin
  • complex siderophores which under conditions of iron limitation, are secreted into the host extracellular environment where they chelate iron, and the resulting ferri-pyoverdine complexes are transported back into the bacteria by a cell surface receptor protein.
Meyer et al., 1996; Takase et al., 2000
Alkaline protease
  • Type-I secreted protein which may play a role early during infection before inflammatory tissue damage
  • linked to corneal infections
Matsumoto, 2004; Van Delden, 2004
Endoprotease (PrpL)
  • hydrolyzes casein, lactoferrin, transferrin, elastin, and decorin
  • contributes to persistance in a model of chronic pulmonary infection
Wilderman et al., 2001

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Appendix 4: LD50 values for P. aeruginosa and its toxins

Pseudomonas aeruginosa



golden apple snail (Pomacea canaliculata)

greater wax moth larvae (Galleria mellonella)

2.7x107 cfu (intranasal injection)

1.6x106 cfu/mouse

(intramuscular injection)

<103 (intratracheal)

3.09x104 - 1.35x106 cfu/ml (72 h LC50 – 5 strains)

7x104 cells (pho23), injected through cuticle



Strain 359 (Serotype 1)

Strain 2915 (Seroptype 7)


21.2.1, B1.1, P1, P2


George et al., 1991

Tamura et al., 1992

Long et al., 1980

Chobchuenchom and Bhumiratana, 2003 

Jander et al., 2000

haemolytic phospolipase C (PlcH)



5 µg/mouse (intraperitoneal)

<2 ng/embryo


PAO1 derivative ADD1976

Berk et al., 1987

Vasil et al., 2009

alkaline proteasemouse

375 µg (IV injection)

7.5 µg/mouse

Strain designation not provided

Strain designation not provided

Nicas & Iglewski, 1986

Hirakata et al., 1999


300 µg (IV injection)

1.2 µg/mouse

Strain designation not provided

Strain designation not provided

Nicas & Iglewski, 1986

Hirakata et al., 1999

exotoxin A

silkworm larvae (Bombyx mori)


0.14 µg/g

0.2 µg (IP injection)

0.06 µg (IV injection)

PAO1 (ATCC 15692)



Hossain et al., 2006

Liu, 1973.

Callahan, 1976

phenazinenematode (C. elegans)

Soil: (LC50)

>2000 mg/kg dw (24 and 48 h)

Aquatic: (LC50)

54.7 mg/L (24 h); 10.8 mg/L (48h)

Chemically synthesizedSochová et al., 2007
pyocyaninsilkworm (Bombyx mori)9.52 μg/larvaPAO1Chieda et al., 2007
rhamnolipidmouse5 mg/kg (IP injection)Strain designation not providedNicas & Iglewski, 1986

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Appendix 5A: Pathogenicity/toxicity to plants, invertebrates and vertebrates (controlled studies)


Arabidopsis thaliana

6-week old plants

  • up to 107 cfu injected per cm2 of leaf tissue
  • 75 strains of clinical and environmental origin were tested
  • no strain designations given
  • strains were from the University of California’s (Berkely) culture collection
  • only PA14 (human isolate) and PA29 (plant isolate) of the 75 strains elicited severe soft-rot symptoms at 9.0 x 106cfu and 2.7 x 107cfu, respectively
Rahme et al., 1995

Arabidopsis thaliana


sweet basil

(Ocimum basilicum)

25-day old plants

  • no inoculate concentration given (OD600= 0.02 at the time of inoculation)
  • roots severed to allow strains PAO1 and PA14 entry past cell wall
  • PAO1
  • PA14
  • roots and leaves near base affected 2 – 3 days post inoculation, spread to top of plant on day 4
  • mortality 7 days post-inoculation
Walker et al., 2004
Arabidopsis thaliana
  • leaves soaked in bacterial suspension(103cfu/ml)
  • PA14
  • maceration and collapse of leaf 4 – 5 days post-infection
Rahme et al., 2000
Alfalfa (variety 57Q77)
  • seedling leaves were inoculated with 10 μl of bacterial suspensions (1 × 103 cells) using 20-gauage needle
  • leaves were incubated for 7 days
  • PAO1
  • FRD1, DO326, DO60, DO139, DO133 (cystic fibrosis isolates)
  • ENV2, ENV48, ENV8, ENV46 (environmental isolates)
  • necrosis and tissue maceration seen at day 6
  • 95% of seedlings inoculated with PAO1
  • 70% of seedlings inoculated with FRD1
  • 3/4 other CFisolates produced disease symptoms in 50% of the plants
  • 3/4 environmental isolates caused symptoms in 75% of the seedlings
  • as few as 20 bacterial cells of PAO1 or FRD1 were sufficient to infect some seedlings and produce disease
Silo-Suh et al., 2002
Lettuce (Lactuca sativa var. capitata L.)
  • leaf segments were placed onto sterile petri dishes and inoculated with 5:l of the bacterial suspension at various concentrations (102, 104, 106 and 107 cfu/ml)
  • new strains were isolated from hospitals and medical institutions from several cities in Colombia, South America (designated 1C-5C) and from soil and water samples (designated 6E-10E)
  • positive control: PA01
  • necrotic lesions were observed on leafs inoculated with 107 cfu/ml of either clinical or environmental isolates
Vives-Flórez & Garnica, 2006
red clover and red fescue. ATCC 31480No adverse effect on seedling emergence, shoot and root length and dry mass of red clover and red fescue.Princz, 2010
barley ATCC 700370No adverse effect on seedling emergence, shoot and root length and dry mass of barley.Princz, 2010
red clover and northern wheatgrass.   ATCC 700371No adverse effect on seedling emergence, shoot and root length and dry mass of red clover and northern wheatgrass.Princz, 2010
soil nematode (Caenorhabditis elegans)
  • nematodes were placed on two types of media containing P. aeruginosa:
  • in low-nutrient media
  • in high-osmolarity media
  • no cfu values given
  • transposon mutants of PA14
  • speed of mortality depended on the type of media used to grow PA14 mutants
  • on low-nutrient media, C. elegans death occurs over the course of several days
  • on high-osmolarity media, C. elegans death occurs over the course of several hours

Tan et al.,


wax moth larvae (Galleria mellonella)
  • up to 1 x 104 cfu was injected into larvae
  • PA14
  • bacterial density in dead larvae was approximately 109 bacteria/g body weight
Jander et al., 1995
  • strains from diseased humans and animals used for inoculation of bees
  • two experiments at 25°C
  • 50 bees fed 24-h broth culture in sugar syrup
  • 50 bees immersed in 24-h broth culture
  • control: 50 bees fed sugar syrup and water
  • no specific mention of a control group that was immersed in liquid not containing bacterial culture
  • no strain designation provided
  • immersed bees: 80% fatality after 48 hours.
  • fed bees:
    fatality occurred 72-96 hours after inoculation
Tomaszewska, 1971

southern pine beetle

(Dendroctonus frontalis)

  • orally inoculated healthy Southern pine beetles
  • strain was isolated from a diseased southern pine beetle
  • 32 of 50 larvae injected died
Moore, 1972

fruit fly (Drosophila melanogaster)

2 - 4 day old adult female flies

  • pricked with needle dipped in a P. aeruginosa PAO1 culture (400-2000 cells)
  • PAO1
  • flies dead 16 - 28 hours after pricking
  • titre measured in dead flies was 1x106 to 40 x106 cfu
D’Argenio et al., 2001

tobacco hornworm larvae (Manduca sexta)

second day fifth instar larvae

  • injected with strains 9027 (7 x107 cfu) or P11-1 (low dose: 5 x104 cfu or high dose: 2 x107)
  • 9027
  • P11-1
  • no cytotoxic effects with strain 9027
  • Strain P11-1 low dose: decreased viability of hemacytes at 44 hours post-injection and increase in hemacyte vacuolization at 56 hours post-injection
  • Strain P11-1 high dose: advanced time of appearance of significantly elevated vacuolization to 16 hours post-injection and of significantly decreased hemocyte viability to 20 hours post-injection
Horohov & Dunn, 1984

silkworm larvae (Bombyx mori)

fourth instar larvae

  • (5/dilution, 3 replicates) injected with 106, 105,104,103 cells
  • PAO1
  • 100%, 100%, 90%, 50% mortality, respectively, within 72 hours
Iiyama et al., 2007


(Helix sp.)

  • 66 snails injected with 10 x 108 cells per gram snail
  • OT97
  • mortality was 92% (61 snails) after a week
Bayne, 1980
springtails and earthworms.     
  • ATCC 31480
  • No adverse effect on adult mortality or juvenile reproduction of springtails and earthworms.
  • Strain persisted for at least 62 days in agricultural soil. Studies for persistence in water on-going
Princz, 2010
  • ATCC 700370
  • No adverse effect on adult mortality or juvenile reproduction of springtails. Strain persisted for at least 122 days in agricultural soil.
Princz, 2010
  • ATCC 700371
  • No adverse effect on adult mortality or juvenile reproduction of springtails.
  • Strain persisted for at least 126 days in agricultural soil.
Princz, 2010

broiler chicks (white leghorn)

1-day old chicks

  • injected subcutaneously with P. aeruginosa cultures (101 or 102 cfu/bird)
  • n=10 per concentration therefore per strain, 20 birds were tested
  • E-00-1963
  • E-00-1964
  • E-00-1965
  • E-00-1996
  • E-00-1997
  • 14 days post inoculation mortality (inoculum at 101/102 cfu/bird):
  • strain E-00-1963: 0/0
  • strain E-00-1964: 1/4
  • strain E-00-1965: 9/9
  • strain E-00-1996: 3/3
  • strain E-00-1997: 2/5
  • saline: 0/0
  • no injection: 0/0
Walker et al., 2002
white leghorn chickens (male)
  • 1 mL (1010 cfu/mL) injected intraperitoneally into 4-week-old male chickens
  • 10 isolates of P. aeruginosa each injected into 10 chickens
  • no strain designations were given
  • strains were isolated from the respiratory tracts of sick birds suffering from a long-lasting respiratory syndrome or from bone marrow of dead birds from the southern part of Taiwan
  • 58% mortality 1 week post-inoculation.
  • 2-10 of the ten birds in each group died.
Lin et al., 1993
  • skin-burn model.
  • 103 cells injected intramuscularly into burned mice
  • PA14
  • 17/22 mice died, 10 days after injection.
Rahme et al., 1995

mice (CD-1)

60-day old male

  • 1 x109 cfu by gavage
  • animals were sacrificed 14 days post-exposure
  • strains: BC16, BC17, BC18
  • isolated from a commercial microbial product designed for PCB degradation
  • no morbidity or mortality during study.
  • bacteria not detectable in intestines 14 days post-single exposure
  • detectable on mice with repeated exposure due to coprophagy (2.6 - 4 x104 cfu/g intestine)
George et al., 1989

mice (CD-1)

30-day old male

  • 1.61 x 103 to 2.17 x 109 cfu P. aeruginosa injected intranasally
·    AC869

·    1.61x103 cfu resulted in no mortality or observed morbidity for 14 day study period

·     1.61 x 107 cfu resulted in slight morbidity within 3 to 4 days after dose

·    2.17x109 cfu resulted in 100% mortality within 24 to 36 h post-injection

George et al., 1991
  • 12 healthy beagles of both sexes were used
  • both eyes were surgically wounded
  • each eye was inoculated intrastromally with 107cfu
  • no strain designation given
  • strain used was isolated from a dog with an infected draining femoral fracture
  • all eyes showed active keratitis
  • Pseudomonas obtained from all corneas 12 hours post-inoculation
Wyman et al., 1983
frogs (Rana pipiens)
  • 0.1 mL of culture dilution by intraperitoneal inoculation (results in systemic distribution of the pathogen)
  • frogs were kept at 22 or 29°C
  • ATCC 27853
  • P. aeruginosa had no significant effect on mortality when administered at low treatment temperatures
  • 12 out of 15 frogs died at higher treatment temperatures
Brodkin et al., 1992
mink (Sapphire)
  • each test strain cultured on nutrient agar medium at 37°C for 18 h
  • 0.5 mL of a 10-fold dilution was noculated intranasally
  • no CFU/mL specified
  • NC-5 (serotype 5)
  • strain No. 5 (serotype 8)
  • in mink that died (2 of 14 for strain NC-5, 18 of 24 for strain No. 5), death occurred between 18 and 66 hours post inoculation
Shimizu et al., 1974
  • ATCC 31480
  • BALB/c mouse exposures showed transient shock-like symptoms. Presence of pyrogenic cytokines in lungs and sera. Neutrophils infiltration into lungs. This strain induced higher responses than the other DSL-listed P. aeruginosa strains.
Preliminary EC HC results
  • ATCC 700370
  • BALB/c mouse exposures showed transient shock-like symptoms. Presence of pyrogenic cytokines in lungs and sera. Neutrophils infiltration into lungs.
Preliminary EC HC research results
  • ATCC 700371
  • BALB/c mouse exposures showed transient shock-like symptoms. Presence of pyrogenic cytokines in lungs and sera. Granulocyte infiltration into lungs.
Preliminary EC HC research results
zebrafish (Danio rerio)
  • 1 or 2 nL of bacterial cells were microinjected into the yolk circulation valley
  • doses tested were 1700, 3000 and 6000 CFU
  • PA14
  • injection of 1700 cells at the 28 hpf developmental stage resulted in death of all infected embryos by ~48 hrs postinfection
  • at the 50 hpf developmental stage, >4500 CFU were required to achieve 100% lethality
Clatworthy et al., 2009

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Appendix 5B: Pathogenicity/toxicity to vertebrates in natural settings

Cases where P. aeruginosa was isolated from animals showing disease symptoms in a natural setting.


mallard ducklings

(Anas platyrhynchos)

  • 9 salt glands in 8 animals with granulomas examined
  • no strain designation given
  • P. aeruginosa most common bacterial species isolated (4 of 9 infected glands)
  • at least 2 biochemically distinct strains responsible
  • granulomatous inflammation of salt glands occurs in 1% of ducklings
  • lesions detected in 2 to 23 day old ducklings
Klopfeisch et al., 2005
  • 18 flocks from 9 producers examined
  • no strain designation given
  • cellulitis on legs or caudal thoracic area
  • 37 of 26670 (0.14%) affected
  • bacteria isolated from 12 of 25 randomly selected birds
  • P. aeruginosa isolated from 3 of the 12 (found in mixed culture with Proteus mirabilis)
Gomis et al., 2002

saker falcons

(Falco cherrug)

- species not found in Canada but anatum peregrine falcon (Falco peregrinus anatum) is a threatened species in Canada

  • stomatitis in 12 captive falcons from 2 different collections
  • no strain designation given
  • P. aeruginosa isolated from all 12 falcons
  • all with a history of mild to moderate trichomonal infections 3 to 4 weeks prior to examination
  • birds also under stress due to training and hunting season
Samour, 2000
  • mastitis outbreak in 11 dairy herds
  • a total of 50 Pseudomonas isolates were used in this study
  • 14 controls, including P. aeruginosa ATCC 27853 and Pseudomonas spp. isolated from a variety of clinical cases
  • 36 of the isolates obtained from the bovine mastitis outbreak were identified as P. aeruginosa
  • P. aeruginosa found to be causative agent
  • P. aeruginosa contaminated wipes rubbed on teat and bacteria introduced into lumen via nozzle of DCT antibiotic tube
Daly et al., 1999
  • 1365 cows with mastitis examined over 31 years
  • no strain designation given
  • 88% culture positive
  • P. aeruginosa isolated in 7.5% of cases
Kivaria & Noordhuizen, 2007
dorset horn rams
  • dermatitis
  • P. aeruginosa isolated from lesions
  • 6 of 12 animals died
  • scale formation on legs, lesions spread over body
cited by Hungerford, 1990

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Appendix 6: Selected outbreaks caused by P. aeruginosa reported in the literature

YearPlaceType of Infection
Not givenUniversity of Iowa Hospitals and ClinicsOutbreak of P. aeruginosa blood stream infections in 7 patients with hematological malignancies caused by a contaminated drain in a whirlpool bathtub. Mortality rate was 71.4% (Berrouane et al., 2000).
1975 to 1985US and CanadaA total of 36 outbreaks of P. aeruginosafolliculitis associated with the use of whirlpools and hot tubs, and to a lesser extent with the use of swimming pools have been reported with increasing frequency during the winter months (Ratnam et al., 1986).
1988Bergamo, ItalyOutbreak of P. aeruginosa infections in neutropenic patients admitted to the Haematological Wards of "Ospedali Riuniti”. Out of 11 cases of P. aeruginosainfections, 8 were bacteraemia. Of these, 7 died within a few days of onset (mortality rate of 87.5%) (Grigis et al., 1993).
1996Royal Women's Hospital, AustraliaOver a 10-month period, 24 newborns were infected by P. aeruginosa (resistant to ticarcillin, timentin). There were extensive morbidity and mortality (38%) associated with the infections, which presented as septicemia, pneumonia, meningitis conjunctivitis, otitis externa and conjunctivitis plus otitis externa. In addition, there were 2 pseudo-septicemia and 6 colonized infants, 3 of whom were treated for the presence of P. aeruginosa in endotracheal aspirates (Garland et al. 1996).
1998Edmonton, Canada40 cases of Pseudomonas hot-foot syndrome occurred after children had used a wading pool. In all patients, the first symptom was intense pain in the soles, followed within hours by marked swelling, redness, a sensation of heat, and exquisite pain that made it impossible to bear weight on the affected areas (PHAC, 2001).
1997 to 2000Colorado and Maine, USA103 reported cases of P. aeruginosadermatitis and otitis externa outbreaks associated with swimming pool and hot tub use. Symptoms were not limited to rash; they included diarrhea, vomiting, nausea, fever, fatigue, muscle aches, joint pain, swollen lymph nodes, and subcutaneous nodules on hands and feet (MMWR, 2000).
2001 to 2002Johns Hopkins Hospital Baltimore, USA2 outbreaks of P. aeruginosa infections involving 48 infections of the upper and lower respiratory tracts and bloodstream among 39 of 414 patients who underwent bronchoscopy (9.4%). In 66.7% of these infections, P. aeruginosa was recovered on culture (Srinivasan et al., 2003).

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Appendix 7: Considerations for Levels of Hazard Severity, Exposure and Risk as per Health Canada and Environment Canada’s “Framework for Science-Based Risk Assessment of Micro-organisms regulated under the Canadian Environmental Protection Act, 1999

Considerations for hazard severity (environment)


Considerations that may result in a finding of high hazard include a micro-organism that:

  • Is known as a frank pathogen;
  • Has irreversible adverse effects (e.g., loss of biodiversity, loss of habitat, serious disease);
  • Has significant uncertainty in the identification, characterization or possible effects.

Considerations that may result in a finding of medium hazard include a micro-organism that:

  • Is known as an opportunistic non-human pathogen or for which there is some evidence in the literature of pathogenicity/toxicity;
  • · Has some adverse but reversible or self-resolving effects.

Considerations that may result in a finding of low hazard include a micro-organism that:

  • Is not known to be a non-human pathogen;
  • Is well characterized and identified with no adverse ecological effects known;
  • May have theoretical negative impacts for a short period but no predicted long term effect for microbial, plant and/or animal populations or ecosystems;
  • Has a history of safe use over several years.

Considerations for hazard severity (human health)


Considerations that may result in a finding of high hazard include a micro-organism for which:

  • Disease in healthy humans is severe, of longer duration and/or sequelae may result;
  • Disease in susceptible humans may be lethal;
  • Potential for horizontal transmission/community-acquired infection;
  • Lethal or severe effects in laboratory mammals at maximum hazard/challenge dose trigger multiple-dose testing.

Considerations that may result in a finding of medium hazard include:

  • Case reports of human disease in the scientific literature are limited to susceptible populations or are rare, localized and rapidly self-resolving in healthy humans;
  • Low potential for horizontal transmission;
  • Effects at maximum hazard/challenge dose in laboratory mammals are not lethal, and are limited to invasive exposure routes (i.e., intraperitoneal, intravenous, intratracheal) or are mild and rapidly self-resolving.

Considerations that may result in a finding of low hazard include:

  • No case reports of human disease in the scientific literature, or case reports associated with predisposing factors are rare and without potential for secondary transmission and any effects are mostly mild, asymptomatic, or benign.
  • No adverse effects seen at maximum challenge dose in laboratory mammals by any route of exposure.

Considerations / examples for level of exposure (environment and human health)


Considerations that may result in a finding of high exposure include a micro-organism for which:

  • The release quantity, duration and/or frequency are high.
  • The organism is likely to survive, persist, disperse proliferate and become established in the environment.
  • Dispersal or transport to other environmental compartments is likely.
  • The nature of release makes it likely that susceptible living organisms or ecosystems will be exposed and/or that releases will extend beyond a region or single ecosystem.
  • In relation to exposed organisms, routes of exposure are permissive of toxic or pathogenic effects in susceptible organisms.

Considerations that may result in a finding of medium exposure include a micro-organism for which:

  • It is released into the environment, but quantity, duration and/or frequency of release is moderate.
  • It may persist in the environment, but in low numbers.
  • The potential for dispersal/transport is limited.
  • The nature of release is such that some susceptible living organisms may be exposed.
  • In relation to exposed organisms, routes of exposure are not expected to favour toxic or pathogenic effects.

Considerations that may result in a finding of low exposure include a micro-organism for which:

  • It is no longer in use.
  • It is used in containment (no intentional release).
  • The nature of release and/or the biology of the micro-organism are expected to contain the micro-organism such that susceptible populations or ecosystems are not exposed.
  • Low quantity, duration and frequency of release of micro-organisms that are not expected to survive, persist, disperse or proliferate in the environment where released.

Considerations for level of risk characterization

HighA determination of high risk implies that severe, enduring or widespread adverse effects are probable for exposure scenarios predicted from known, foreseeable or intended uses. A conclusion of CEPA-toxic would result and control measures or risk management would be recommended.
MediumA determination of medium risk implies that adverse effects predicted for probable exposure scenarios may be moderate and self-resolving. The conclusion (CEPA toxic or not) is chosen based on the particulars of the case. If the conclusion is not CEPA-toxic, for intended (proposed) use(s) or exposure scenario(s) but, under another significant new activity, may become toxic, application of the SNAcprovision may be recommended to allow for the assessment of new uses/activities.
LowA determination of low risk implies that any adverse effects predicted for probable exposure scenarios are rare, or mild and self-resolving. The conclusion would be not CEPA toxic, and SNAc provisions may or may not be applied.


[1] Refer to Appendix 7 for the definitions of hazard levels.
[2] Refer to Appendix 7 for the definitions of exposure levels.
[3] Refer to Appendix 7 for the definitions for levels of risk.
[4] Refer to Appendix 4 for LD50 values for some of the toxins.
[*] Data generated by Health Canada’s Healthy Environments and Consumer Safety Branch.

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