ARS | Publication request: Prevalence and characterization of non-O157 Shiga toxin-producing Escherichia coli isolated from feedlot and cull dairy and beef herd cattle

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: January 31, 2012
Publication Date: N/A

Technical Abstract: Ruminants, and especially cattle, are considered the primary reservoir of Shiga-toxin producing Escherichia coli (STEC) and contaminated beef products are considered one vehicle of transmission to humans. However, cattle entering the beef harvest process may originate in very different production systems and are destined for different beef products. Feedlot cattle are young animals that originate from densely populated confined animal feeding operations and are primarily fabricated into whole muscle beef cuts. Culled dairy and beef cattle are significantly older when harvested and are primarily destined for ground beef. Cull beef cattle are typically pasture-fed and maintained at a lower density of animals than dairy cattle. The objective of these studies was to determine whether these differences in production system affect the prevalence and/or type of STEC present in the cattle. Feces was collected from colons of cattle from these three production systems (n = 400 each) at harvest and assessed for the prevalence of STEC based on the detection of stx1 and stx2 by PCR. STEC screened positive feces was then subjected to rounds of culture isolation by direct plating to selective agar. Prevalence of stx was different (P<0.05) between the 3 groups of cattle (Feedlot = 68.5%, Cull Beef = 59.0%, and Cull Dairy = 50.5%). A STEC isolate was recovered from approximately 20% of the samples that had been screened as positive for a STEC. STEC, including serotypes O26, O103, O111, and O145 containing stx, intimin, and other genetic markers of increased virulence were isolated from cattle from all sources. Overall, significantly more pathogenic STEC were identified in cull dairy cattle (3.5%) than cull beef cattle (1.0%) (P<0.05) but feedlot cattle (1.5%) were not different from either of the cull cattle groups. Although this study is based on a limited population, the results suggest cull dairy cattle may harbor greater numbers of pathogenic STEC than other types of cattle. This intriguing observation warrants further study and manifests the need for a much larger comprehensive study.