title: Prevalence of Shiga toxin-producing Escherichia coli and associated virulence genes in feces of commercial feedlot cattle.
abstract: The objective of this study was to determine the prevalence of Shiga toxin-producing Escherichia coli (STEC) serogroups and associated virulence genes in feces of commercial feedlot cattle. During March to May 2011, fecal samples were collected from individual cattle (n=960) in 10 cohorts (cattle subpopulations within a feedlot) comprising 17,148 total steers that originated from 48 backgrounding operations in six U.S. states. Fecal samples were enriched in E. coli broth and subjected to two detection protocols: (1) an 11-gene multiplex polymerase chain reaction (PCR) that identifies seven O serogroups (O26, O45, O103, O111, O121, O145, and O157) and four virulence genes (stx1, stx2, eae, and ehxA) applied to extracted total DNA ("direct PCR"); and (2) cultural procedures that involve immunomagnetic separation (IMS) with O26, O103, and O111 beads, plating on a nondifferential MacConkey agar, followed by the multiplex PCR of pooled colonies ("culture-based method"). Generalized linear mixed models were used to adjust prevalence estimates for clustering. Based on direct PCR detection, O157 (49.9%) was the most prevalent O serogroup followed by O26 (20.3%), O103 (11.8%), O121 (10.7%), O45 (10.4%), O145 (2.8%), and O111 (0.8%). Cumulative adjusted prevalence estimates were 22.3, 24.6, and 0.01% for O26, O103, and O111 serogroups, respectively, based on culture-based methods. However, prevalence varied significantly by cohort (p-values<0.05) for O26, O121, and O157 based on direct PCR, and for O26, O103, and O111 serogroups based on culture-based methods. Results of this study indicate that all seven STEC serogroups were identified in feedlot cattle feces, with O157, O26, and O103 being the most prevalent serogroups. A substantial proportion of serogroup-positive samples did not harbor Shiga toxin genes; thus, additional elucidation of the potential human health risk is required. Further evaluation of diagnostic methods for non-O157 STEC is needed given their impact on prevalence estimation.
authors.affiliation: Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University , Manhattan, Kansas.
authors.forename: Natalia
authors.initials: N
authors.lastname: Cernicchiaro
authors.forename: Charley A
authors.initials: CA
authors.lastname: Cull
authors.forename: Zachary D
authors.initials: ZD
authors.lastname: Paddock
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Shi
authors.forename: Jianfa
authors.initials: J
authors.lastname: Bai
authors.forename: Tiruvoor G
authors.initials: TG
authors.lastname: Nagaraja
authors.forename: David G
authors.initials: DG
authors.lastname: Renter
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D015331:Cohort Studies; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D005516:Food Microbiology; D005517:Foodborne Diseases / Q000517:prevention & control; D006801:Humans; D008297:Male; D060885:Multiplex Polymerase Chain Reaction / Q000662:veterinary; D019081:O Antigens / Q000235:genetics*; D015995:Prevalence; D022621:Shiga Toxin / Q000235:genetics; D054323:Shiga-Toxigenic Escherichia coli / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification* / Q000472:pathogenicity; D013045:Species Specificity; D014481:United States / Q000453:epidemiology; D014774:Virulence
chemical_list: D019081:O Antigens; D022621:Shiga Toxin