Large scale analysis of virulence genes in Escherichia coli strains isolated from Avalon Bay, CA

Abstract

Contamination of recreational waters with E. coli and Enterococcus sp. is a widespread problem resulting in beach closures and loss of recreational activity. While E. coli is frequently used as an indicator of fecal contamination, and has been extensively measured in waterways, few studies have examined the presence of potentially pathogenic E. coli strains in beach waters. In this study, a combination of high-throughput, robot-assisted colony hybridization and PCR-based analyses were used to determine the genomic composition and frequency of virulence genes present in E. coli isolated from beach water in Avalon Bay, Santa Catalina Island, CA. A total of 24,493 E. coli isolates were collected from two sites at a popular swimming beach between August through September 2007 and from July through August 2008. All isolates were examined for the presence of shiga-like toxins (stx1/stx2), intimin (eaeA), and enterotoxins (ST/LT). Of the 24,493 isolates examined, 3.6% contained the eaeA gene, indicating that these isolates were potential EPEC strains. On five dates, however, greater than 10% of the strains were potential EPEC, suggesting that incidence of virulence genes at this beach has a strong temporal component. No STEC or ETEC isolates were detected, and only eight (<1.0%) of the potential EPEC isolates were found to carry the EAF plasmid. The potential EPEC isolates mainly belonged to E. coli phylogenetic groups B1 or B2, and carried the beta intimin subtype. DNA fingerprint analyses of the potential EPEC strains indicated that the isolates belonged to several genetically diverse groups, although clonal isolates were frequently detected. While the presence of virulence genes alone cannot be used to determine the pathogenicity of strains, results from this study show that potential EPEC strains can be found in marine beach water and their presence needs to be considered as one of the factors used in decisions concerning beach closures.

Antibiotic resistance and virulence genes in coliform water isolates

“…Typical EPEC strains carry the LEE pathogenicity island, which encodes for several virulence factors, including intimin (eaeA) and the plasmid encoded bundle forming pilus (bfp) which mediates adhesion to intestinal epithelial cells (Kaper et al, 2004;Hamilton et al, 2010). In this study, the bfp gene was not detected along with eaeA in any of isolates.…”

“…Out of these nine isolates, five could be allocated to the phylogenetic groups B2 and D (noncommensal (Sidhu et al, 2013;Chen et al, 2011;Hamilton et al, 2010;Koczura et al, 2013). Antibiotic resistant shiga toxin producing E. coli (STEC) and ETEC were detected in surface water samples from River Ganga and River Gomti in India (Ram et al, 2008).…”

“…Antibiotic resistant shiga toxin producing E. coli (STEC) and ETEC were detected in surface water samples from River Ganga and River Gomti in India (Ram et al, 2008). Frequent detection of potential EPEC strains from contaminated marine recreational water in Avalon Bay, California USA has also reported (Hamilton et al, 2010). In another study, about a quarter of the E. coli isolated from Minjiang River in China carried at least one of the 11 virulence genes evaluated (Chen et al, 2011).…”

Occurrence of Intestinal and Extraintestinal Virulence Genes in Escherichia coli Isolates from Rainwater Tanks in Southeast Queensland, Australia

“…coli pathotypes such as STEC, EPEC, ETEC, and ExPEC and their associated VGs were selected in this study, as other studies have reported the presence of these pathotypes, originating from sewage and/or animal feces, in environmental water (23,24,25,38,46). Overall, 30 (15%) of 200 isolates from eight tanks were positive for the eaeA gene, which belongs to STEC or EPEC (25). However, none of the isolates was positive for the stx 1 , stx 2 , and hlyA genes.…”

“…E. coli O157:H7 is known to harbor stx 1 , stx 2 , or both toxin genes along with the eaeA gene (9,37,43). All eaeA-positive strains were further tested for the presence of the bfpA (bundle-forming pilus) gene, which indicates whether the strains are EPEC or not (25). None of these strains were positive for the bfpA gene, and therefore these strains can be classified as atypical EPEC (aEPEC), as suggested by Kaper et al (35).…”