Occurrence of Genes Associated with Enterotoxigenic and Enterohemorrhagic Escherichia coli in Agricultural Waste Lagoons

c Escherichia coli isolates (n ‫؍‬ 300) collected from six sites in subtropical Brisbane, Australia, prior to and after storm events were tested for the presence of 11 virulence genes (VGs) specific to diarrheagenic pathotypes. The presence of eaeA, stx 1 , stx 2 , and ehxA genes specific for the enterohemorrhagic E. coli (EHEC) pathotype was detected in 56%, 6%, 10%, and 13% of isolates, respectively. The VGs astA (69%) and aggR (29%), carried by enteroaggregative (EAEC) pathotypes, were frequently detected in E. coli isolates. The enteropathogenic E. coli (EPEC) gene bfp was detected in 24% of isolates. In addition, enteroinvasive E. coli (EIEC) VG ipaH was also detected in 14% of isolates. During dry periods, isolates belonging to the EAEC pathotype were most commonly detected (23%), followed by EHEC (11%) and EPEC (11%). Conversely, a more uniform prevalence of pathotypes, EPEC (14%), EAEC (12%), EIEC (10%), EHEC (7%), and ETEC (7%), was observed after the storm events. The results of this study highlight the widespread occurrence of potentially diarrheagenic pathotypes in the urban aquatic ecosystems. While the presence of VGs in E. coli isolates alone is insufficient to determine pathogenicity, the presence of diarrheagenic E. coli pathotypes in high frequency after the storm events could lead to increased health risks if untreated storm water were to be used for nonpotable purposes and recreational activities. Storm events can result in mobilization and transport of fecal contaminants from point sources, such as urban wastewater treatment plants, and nonpoint sources, in particular animal fecal material, to receiving water bodies. The presence of fecal contamination in rivers, lakes, and creeks can lead to the degradation of water quality and subsequently result in the water becoming unfit for potable/nonpotable uses, aquaculture, and recreational activities such as swimming and fishing (1-4).Escherichia coli and Enterococcus spp. commonly found in mammalian feces have been traditionally used as indicators of fecal pollution in fresh and marine waters (5, 6). After storm events, a severalfold increase in the fecal indicator bacteria (FIB) numbers occur in the surface waters (7-9). There may be several sources of E. coli that contribute to sudden increases in numbers of this bacterium in waterways, including sewage overflows, farm animals, pets, and birds. The elevated microbial contaminants in storm runoff (7, 10) and subsequently in receiving water bodies may pose a serious public health risk. Disease outbreaks related to exposure to contaminated freshwater are well documented (11)(12)(13)(14). Exposure to recreational water has been linked to high numbers (21 out of 31) of reported E. coli O157:H7 disease outbreaks in the United States from 1982 to 2002 (15). Despite the significant disease burden linked to contaminated water exposure, the prevalence of E. coli pathotypes in the urban aquatic environment is not well characterized.The majority of E. coli strains are commensal; however, some strains have ...

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confidence: 90%

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confidence: 98%

Occurrence of Virulence Genes Associated with Diarrheagenic Pathotypes in Escherichia coli Isolates from Surface Water

Sidhu

Ahmed

Hodgers

et al. 2013

“…These methods are useful for identification and tracking E. coli O157:H7 and other E. coli strains from different sources (19,35); however, they do not assess the pathogenic potential of the strains. Research has shown that the prevalence of potentially virulent E. coli strains or their associated genes may in the environment may be greater than previously realized (9)(10)(11). However, none of these studies tested the virulence potential of environmental bacteria carrying these genes.…”

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confidence: 91%

Cytotoxicity Potential and Genotypic Characterization of Escherichia coli Isolates from Environmental and Food Sources

Maldonado¹,

Fiser

Nakatsu

et al. 2005

The presence of Escherichia coli isolates in the environment is a potential source of contamination of food and water supplies. Moreover, these isolates may harbor virulence genes that can be a source of new forms of pathogenic strains. Here, using multiplex PCR, we examined the presence of virulence gene markers (stx 1 , stx 2 , eaeA, hlyA) in 1,698 environmental isolates of E. coli and 81 isolates from food and clinical sources. The PCR analysis showed that ϳ5% (79 of 1,698) of the total environmental isolates and 96% (79 of 81) of the food and clinical isolates were positive for at least one of the genes. Of the food and clinical isolates, 84% (68 of 81 isolates) were positive for all four genes. Of the subset of environmental isolates chosen for further analysis, 16% (13 of 79 isolates) were positive for stx 2 and 84% (66 of 79 isolates) were positive for eaeA; 16 of the latter strains were also positive for hlyA. The pathogenic potentials of 174 isolates (81 isolates from food and clinical sources and 93 isolates from environmental sources) were tested by using a cytotoxicity assay based on lactate dehydrogenase release from Vero cells. In general, 97% (79 of 81) of the food and clinical isolates and 41% (39 of 93) of the environmental isolates exhibited positive cytotoxicity. High cytotoxicity values correlated to the presence of stx genes. The majority of hly-positive but stx-negative environmental isolates also exhibited a certain degree of cytotoxicity. Isolates were also tested for sorbitol utilization and were genotyped by ribotyping and by repetitive extragenic palindromic PCR (REP-PCR) as potential means of quickly identifying virulent strains from the environment, but none of these methods could be used to distinguish cytotoxic environmental isolates. Only 31% of the isolates were negative for sorbitol fermentation, and none of the isolates had common ribotypes or REP-PCR fingerprints. This study suggests that overall higher cytotoxicity values correlated with the production of stx genes, and the majority of hly-positive but stx-negative environmental isolates also exhibited a certain degree of cytotoxicity. This study demonstrated that there is widespread distribution of potentially virulent E. coli strains in the environment that may be a cause of concern for human health.

“…In this context, specific virotypes can tentatively be ascribed to environmental isolates on the basis of virulence gene profiling, the assumption being that specific complements of virulence genes are associated with the ability to cause specific diseases (6)(7)(8). The virulence gene profiling approach has been used to characterize the seasonal and spatial distribution of waterborne E. coli that are potentially pathogenic to humans or livestock and to identify associations in virotype distribution within catchments with variation in land use, climate, and the distribution of potential sources of fecal contamination (9)(10)(11)(12)(13)(14)(15). There are, however, practical problems with the tractability of the virulence gene profiling approach.…”

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confidence: 99%

Evaluating the Pathogenic Potential of Environmental Escherichia coli by Using the Caenorhabditis elegans Infection Model

Merkx-Jacques

Coors

Brousseau

et al. 2013

The detection and abundance of Escherichia coli in water is used to monitor and mandate the quality of drinking and recreational water. Distinguishing commensal waterborne E. coli isolates from those that cause diarrhea or extraintestinal disease in humans is important for quantifying human health risk. A DNA microarray was used to evaluate the distribution of virulence genes in 148 E. coli environmental isolates from a watershed in eastern Ontario, Canada, and in eight clinical isolates. Their pathogenic potential was evaluated with Caenorhabditis elegans, and the concordance between the bioassay result and the pathotype deduced by genotyping was explored. Isolates identified as potentially pathogenic on the basis of their complement of virulence genes were significantly more likely to be pathogenic to C. elegans than those determined to be potentially nonpathogenic. A number of isolates that were identified as nonpathogenic on the basis of genotyping were pathogenic in the infection assay, suggesting that genotyping did not capture all potentially pathogenic types. The detection of the adhesin-encoding genes sfaD, focA, and focG, which encode adhesins; of iroN 2 , which encodes a siderophore receptor; of pic, which encodes an autotransporter protein; and of b1432, which encodes a putative transposase, was significantly associated with pathogenicity in the infection assay. Overall, E. coli isolates predicted to be pathogenic on the basis of genotyping were indeed so in the C. elegans infection assay. Furthermore, the detection of C. elegans-infective environmental isolates predicted to be nonpathogenic on the basis of genotyping suggests that there are hitherto-unrecognized virulence factors or combinations thereof that are important in the establishment of infection.