The diversity of Escherichia coli serotypes and biotypes in cattle faeces

If the acquisition of virulence genes (VGs) for pathogenicity were not solely acquired through horizontal gene transfers of pathogenicity islands, transposons, and phages, then clonal clusters of enterotoxigenic Escherichia coli (ETEC) would contain few or even none of the VGs found in strains responsible for extraintestinal infections. To evaluate this possibility, 47 postweaning diarrhea (PWD) ETEC strains from different geographical origins and 158 commensal E. coli isolates from the gastrointestinal tracts of eight group-housed healthy pigs were screened for 36 extraintestinal and 18 enteric VGs using multiplex PCR assays. Of 36 extraintestinal VGs, only 8 were detected (fimH, traT, fyuA, hlyA, kpsMtII, k5, iha, and ompT) in the ETEC collection. Among these, hlyA (␣-hemolysin) and iha (nonhemagglutinating adhesin) occurred significantly more frequently among the ETEC isolates than in the commensal isolates. Clustering analysis based on the VG profiles separated commensal and ETEC isolates and even differentiated serogroup O141 from O149. On the other hand, pulsed-field gel electrophoresis (PFGE) successfully clustered ETEC isolates according to both serotype and geographical origin. In contrast, the commensal isolates were heterogeneous with respect to both serotype and DNA fingerprint. This study has validated the use of VG profiling to examine pathogenic relationships between porcine ETEC isolates. The clonal relationships of these isolates can be further clarified by PFGE fingerprinting. The presence of extraintestinal VGs in porcine ETEC confirmed the hypothesis that individual virulence gene acquisitions can occur concurrently against a background of horizontal gene transfers of pathogenicity islands. Over time, this could enable specific clonotypes to respond to host selection pressure and to evolve into new strains with increased virulence.Enterotoxigenic Escherichia coli (ETEC) is the major cause of postweaning diarrhea (PWD) in weaned pigs. ETEC strains colonize the small intestine with the aid of adhesion factors (e.g., F4 or F18 fimbriae). Once attached, the release of either heat-labile or heat-stable (STa or STb) enterotoxins induces diarrhea by affecting the electrolyte balance of the small intestine. The presence of virulence genes (VGs) encoding these determinants is a key requirement for pathogenicity in ETEC and is generally used to distinguish these pathogens from the nonpathogenic or commensal E. coli normally carried in the intestine (37).Characterization of isolates from outbreaks of PWD has shown that ETEC strains lacking recognized fimbriae, such as F4 and F18, are becoming more common (19,26,44). This may be related to the widespread use of vaccines incorporating fimbriated strains, providing selection pressure for the acquisition and carriage of novel, unrecognized VGs. For example, Noamani et al. (37) found that most of the PWD isolates recovered in the period 1998 to 2001 in Ontario, Canada, were associated with a new type of O149 ETEC, which possessed VGs for STa and an enteroag...

Section: Discussionmentioning

confidence: 99%

“…E. coli isolates were serotyped by the Microbiological Diagnostic Unit, University of Melbourne, Australia, using slide agglutination tests as described previously (5,6). Strains which failed to achieve motility on semisolid medium were considered nonmotile and designated H Ϫ .…”

Section: Methodsmentioning

confidence: 99%

Comparative Analysis of Virulence Genes, Genetic Diversity, and Phylogeny of Commensal and Enterotoxigenic Escherichia coli Isolates from Weaned Pigs

Chapman

Trott

et al. 2007

“…A higher level of unused available nutrients and/or lower resource heterogeneity may result in a lower diversity of microbes and an increased susceptibility to pathogen invasion. Fewer bovine commensal E. coli serotypes were isolated from the feces of cattle on feedlot/grain diets compared with cattle on pasture/roughage-based diets (4), and some studies concluded that the shedding of E. coli O157:H7 is reduced when cattle are fed a low-energy hay-based diet compared to a highenergy grain-based diet (22,45). We observed higher levels of total dissolved organic carbon and total nitrogen in manure positive for stx 2 , which might be an indication of a possible relationship between the nutrient status of the gut/manure and the presence of verotoxin-producing E. coli virulence factors.…”

Section: Discussionmentioning

confidence: 99%

Prevalence of Shiga Toxin-Producing Escherichia coli stx ₁ , stx ₂ , eaeA , and rfbE Genes and Survival of E. coli O157:H7 in Manure from Organic and Low-Input Conventional Dairy Farms

Franz

Klerks

Vos

et al. 2007

Manure samples were collected from 16 organic (ORG) and 9 low-input conventional (LIC) Dutch dairy farms during August and September 2004 to determine the prevalence of the STEC virulence genes stx 1 (encoding Shiga toxin 1), stx 2 (encoding Shiga toxin 2), and eaeA (encoding intimin), as well as the rfbE gene, which is specific for Escherichia coli O157. The rfbE gene was present at 52% of the farms. The prevalence of rfbE was higher at ORG farms (61%) than at LIC farms (36%), but this was not significant. Relatively more LIC farms were positive for all Shiga toxin-producing E. coli (STEC) virulence genes eaeA, stx 1 , and stx 2 , which form a potentially highly virulent combination. Species richness of Enterobacteriaceae, as determined by DGGE, was significantly lower in manure positive for rfbE. Survival of a green fluorescent protein-expressing E. coli O157:H7 strain was studied in the manure from all farms from which samples were obtained and was modeled by a biphasic decline model. The time needed to reach the detection limit was predominantly determined by the level of native coliforms and the pH (both negative relationships). Initial decline was faster for ORG manure but leveled off earlier, resulting in longer survival than in LIC manure. Although the nonlinear decline curve could theoretically be explained as the cumulative distribution of an underlying distribution of decline kinetics, it is proposed that the observed nonlinear biphasic pattern of the survival curve is the result of changing nutrient status of the manure over time (and thereby changing competition pressure), instead of the presence of subpopulations differing in the level of resistance.Shiga-toxin producing Escherichia coli (STEC) is an important group of zoonotic human pathogens, with E. coli O157 being the best known and most studied serotype (10). STEC strains are generally carried asymptomatically by cattle and shed in their feces, which in turn may serve as a means of maintenance and spread of these pathogens among cattle herds (47). Since the reported increase in food-borne disease associated with the consumption of fresh vegetables (51, 54), the potential contamination of vegetable crops that are grown in fields enriched with manure has raised increasing concern (18, 29, 52). Understanding on-farm survival and spread of human pathogens is of utmost importance in preventing the spread of this organism to the environment, groundwater, food, and crops and subsequently back to cattle.A considerable body of literature exists on the prevalence of STEC on cattle farms and statistically associated management factors which could be used for potential intervention strategies to reduce shedding of these pathogens (2, 53, 57). However, these studies are not unambiguous and have resulted in the identification of only a very few risk factors, like season and cattle age, which are ubiquitous. The direction of influence of the majority of the management practices like feeding regimen and housing conditions remains unclear and is under debate.D...

“…Raccoons living at the zoo and urban sites would likely have had more access to human refuse than raccoons living at the more rural site; however, because we looked only at a small number of raccoons at single urban, rural, and zoo sites in this study, further studies are required to determine if the prevalences of AMR in E. coli isolates from raccoons differ between environments. Serotyping and PFGE typing of E. coli isolates from raccoons that were part of the longitudinal study at the zoo site showed that, similar to other animals, including humans (3,25), individual raccoons can concurrently shed a diverse array of E. coli strains. In addition, we found only two instances where the same serotype of E. coli was detected in the same individual in different months, indicating that there is probably a rapid turnover of E. coli serotypes within individual animals.…”

Section: Discussionmentioning

confidence: 99%

Antimicrobial Resistance in Escherichia coli Isolates from Raccoons (Procyon lotor) in Southern Ontario, Canada

Jardine

Janecko

Allan

et al. 2012

ABSTRACTWe conducted a cross-sectional study to determine the prevalence of antimicrobial resistance (AMR) in fecalEscherichia coliisolates from raccoons (Procyon lotor) living in Ontario, Canada. From June to October 2007, we trapped raccoons in three areas: one primarily urban site around Niagara, one primarily rural site north of Guelph, and one at the Toronto Zoo. In addition, we conducted a longitudinal study at the Toronto Zoo site to investigate the temporal dynamics of fecalE. coliand AMR in raccoons. Reduced susceptibility to ≥1 antimicrobial agent was detected inE. coliisolates from 19% of 16 raccoons at the urban site, 17% of 29 raccoons from the rural site, and 42% of 130 samples collected from 59 raccoons at the zoo site. Raccoons from the zoo site were significantly more likely to shedE. coliwith reduced susceptibility to ≥1 antimicrobial agent than animals from the rural site (odds ratio [OR], 3.41; 95% confidence interval [CI], 1.17 to 12.09;P= 0.02). Resistance to expanded-spectrum cephalosporins (and the associatedblaCMY-2gene) was detected in two animals from the zoo site and one animal from the rural site. Serotyping and pulsed-field gel electrophoresis analysis show that raccoons on the zoo grounds harbor a diverse assemblage ofE. coli, with rapid bacterial turnover within individuals over time. Our study indicates that raccoons may shed resistant bacteria of public health significance and that raccoons have the potential to disseminate these bacteria throughout their environment.