Prevalence of Enterohemorrhagic Escherichia coli on Hides of Beef Feedlot Cattle

Introduction: Intimin-positive serogroup O26, O45, O103, O111, O121, O145, and O157 Shiga toxin-producing E. coli have been declared adulterants in non-intact, raw beef by the USDA-FSIS.  These organisms, also classified as enterohemorrhagic E. coli (EHEC), are spread to carcass surfaces from hides during hide removal at harvest.  

Purpose: The objective of this study was to determine the prevalence of the 7 adulterant types of EHEC (EHEC-7) on the hides of commercial feedlot beef cattle at harvest.

Methods: Twenty-four pens of crossbred finishing cattle from a large commercial feedlot in the Central U.S. were sampled at harvest using a repeated cross-sectional study design from June to August 2013 (24 cattle/pen, 2 pen/week, 12 weeks; n=576).  Hide swab samples were enriched in EC broth, subjected to immunomagnetic separation (IMS), and plated on modified Possé agar. Isolates were tested by multiplex PCR for genes for O-group, Shiga toxin 1 and 2, intimin and enterohemolysin, and DNA from an aliquot of enriched broth was tested by the NeoSEEK™ STEC Detection and Identification test (Neogen^®Corp.).

Results: By NeoSEEK™, the prevalence was EHEC-7, 98.1%; EHEC O26, 0.5%; EHEC O45, 40.8%; EHEC O103, 97.2%; EHEC O111, 4.5%; EHEC O121, 2.4%; EHEC O145, 49.1%; and EHEC O157, 14.4%. By culture, the prevalence was EHEC-7, 1.5%; EHEC O26, 0.6%; EHEC O145, 0.2%; EHEC O157, 0.6%; and EHEC O45, EHEC O103, EHEC O111, and EHEC O121, 0.0%. 

Significance: Based on the NeoSEEK^TM test, the prevalence of EHEC-7 on hides of feedlot beef cattle was extremely high, nearly 100%, with EHEC O103, O145, O45, and O157 the most prevalent. By comparison, the prevalence based on culture was very low, with EHEC O26 and O157 in highest prevalence, followed by EHEC O145.  The data collected in this study will be used to populate a quantitative microbial risk assessment model for these pathogens along the beef chain.