Purpose: The objectives of this study were to: 1) determine the prevalence of EHEC-7 in fecal, hide, and pre-intervention carcass samples from culled dairy cows at harvest, and 2) evaluate detection methods for EHEC-7 in these matrices.
Methods: One hundred culled dairy cows were sampled at harvest (June to July 2014). Matched fecal, hide and carcass samples were enriched in E. coli (EC) broth and by immunomagnetic separation (IMS). Enriched samples were plated on CHROMagarTM STEC and recovered IMS beads were plated on STEC heart infusion washed blood agar with mitomycin-C, CHROMagarTM O157 and USMARC STEC agar. Colonies were tested for Shiga Toxin (stx), EHEC-7 O-groups (wzx, wbq, or rfbE), and intimin (eae) by PCR. Samples with EHEC-7 recovered by any agar were considered culture positive. Enriched samples were tested by NeoSEEKTM (Neogen® Corp.), and the Atlas® EG2 Combo assay (Roka®Bioscience). Agreement between methods was determined by Cohen’s kappa coefficient and McNemar’s Chi-square test.
Results: By culture, EHEC-7 were recovered from 7.0%, 16.0% and 1.0% for feces, hides and carcasses, respectively. By NeoSEEKTM, the prevalence of EHEC-7 was 26.0%, 65.0%, and 7.0% for feces, hides and carcasses, respectively. By Atlas® EG2, 29.0%, 46.0%, and 28.0% were non-O157 EHEC positive and 29.0%, 51.0%, and 3.0% were O157:H7 positive for feces, hides, and carcasses, respectively. Moderate agreement was observed between culture and NeoSEEKTM for detection of EHEC-O26 (Kappa = 0.5773, P < 0.05), EHEC-O121 (Kappa = 0.4975, P < 0.05) and EHEC-O157 (Kappa = 0.4012, P < 0.05). No agreement was observed between other methods.
Significance: Detection of EHEC-7 on carcasses indicates that effective interventions are critical to ensure food safety.