Characterization of Escherichia coli O157:H7 Strains Isolated from Supershedding Cattle

Abstract

Previous reports have indicated that a small proportion of cattle shedding high levels of Escherichia coli O157:H7 is the main source for transmission of this organism between animals. Cattle achieving a fecal shedding status of 10 4 CFU of E. coli O157: H7/gram or greater are now referred to as supershedders. The aim of this study was to investigate the contribution of E. coli O157:H7 strain type to supershedding and to determine if supershedding was restricted to a specific set of E. coli O157:H7 strains. Fecal swabs (n ‫؍‬ 5,086) were collected from cattle at feedlots or during harvest. Supershedders constituted 2.0% of the bovine population tested. Supershedder isolates were characterized by pulsed-field gel electrophoresis (PFGE), phage typing, lineage-specific polymorphism assay (LSPA), Stx-associated bacteriophage insertion (SBI) site determination, and variant analysis of Shiga toxin, tir, and antiterminator Q genes. Isolates representing 52 unique PFGE patterns, 19 phage types, and 12 SBI clusters were obtained from supershedding cattle, indicating that there is no clustering to E. coli O157:H7 genotypes responsible for supershedding. While being isolated directly from cattle, this strain set tended to have higher frequencies of traits associated with human clinical isolates than previously collected bovine isolates with respect to lineage and tir allele, but not for SBI cluster and Q type. We conclude that no exclusive genotype was identified that was common to all supershedder isolates. E scherichia coli O157:H7 is an important food-borne pathogen that poses a serious public health concern and financial burden. Cattle are the principal animal reservoir of E. coli O157:H7, and while the rumen has been shown to harbor this pathogen on occasion, it is found more frequently in the distal portion of the bovine gastrointestinal (GI) tract, with the rectoanal junction (RAJ) identified as the predominant colonization site (1, 2). Once colonized, an animal can shed various concentrations of E. coli O157:H7 organisms in the feces. Among colonized individuals, a small proportion will excrete E. coli O157:H7 at levels of Ն10 4 CFU/g of feces. These animals have been referred to as supershedders and are reported to be responsible for increased transmission of E. coli O157:H7 within cattle production environments as well as having significant effects on contamination of the cattle hide and carcass (3-6).Matthews et al. (7) presented data suggesting that 20% of the E. coli O157:H7 infections in cattle on Scottish farms were responsible for 80% of the transmission of the organism between animals. Another study showed that 9% of the animals shedding E. coli O157:H7 at harvest produced over 96% of the total E. coli O157:H7 fecal load for the group (6). Conversely, feedlot cattle that did not shed E. coli O157:H7 over the course of study were five times more likely to be housed in a pen that did not contain a supershedder (8). In addition, Arthur et al. (3) have shown that 95% of feedlot pens containing at least one sup...

Curli Temper Adherence of Escherichia coli O157:H7 to Squamous Epithelial Cells from the Bovine Recto-Anal Junction in a Strain-Dependent Manner

“…In addition, all SS-O157 and control O157 strains adhered to HEp-2 cells in a "diffuse and moderate" pattern (Table 1). An initial screening on CRI plates confirmed that the control strains were curli-expressing (C ϩ ) strains as reported in other studies (27), but the SS-O157 strains differed in their levels of curli production, with only strains SS-12 and SS-42 appearing to be C ϩ (34,35). Since neither the RSE cell adherence patterns nor the HEp-2 cell adherence patterns of these O157 strains could be associated with their respective curli phenotype (Table 1), it appeared that, in contrast to previous reports (25)(26)(27)29), the adherence was not dependent on the curli fimbriae.…”

“…Eight previously characterized O157 isolates obtained from supershedding cattle were used in this study (34,35). These supershed (SS) O157 isolates included SS-7, SS-12, SS-17, SS-27, SS-42, SS-52, SS-67, and SS-77 (Table 1) (34,35).…”

Comparative Genomics and Immunoinformatics Approach for the Identification of Vaccine Candidates for Enterohemorrhagic Escherichia coli O157:H7

“…Further, the discovery of cattle reservoirs shedding high levels of STEC O157: H7, which has been associated with the transmission between animals and across the human-animal interface (30,31), strongly supports the idea that adoption of vaccination for livestock and/or susceptible individuals will have significant public health benefits, preventing substantial numbers of human STEC O157 cases (32). Therefore, further discovery for EHEC-specific antigens needs to be done to improve existing or to develop novel vaccines.…”

Characterization of Escherichia coli O157:H7 Strains from Contaminated Raw Beef Trim during “High Event Periods”

“…It can be speculated that this would provide a large concentration and volume of strain-specific contamination that would need to be reduced through proper dressing and functional interventions. However, this scenario seems unlikely, because supershedders make up approximately 2% of the cattle population (26), and multiple supershedders likely enter processing plants on a daily basis during high shedding season. As shown in Tables 2 and 3, there is little evidence of incoming cattle hides being contaminated with predominantly one strain type.…”

“…The FSIS isolates had a similar high rate (81.3%) of human illness-associated strain types, indicating that the tir T allele may not be associated specifically with HEP but rather with beef trim in general. It should be noted that the tir T allele was recently found to have a prevalence of 71% among E. coli O157:H7 strains isolated from supershedding cattle (26). More data will be needed to determine if human illnessassociated strains are associated with beef trim and if supershedding plays a role in such an association.…”