Seasonal prevalence of Shiga toxin-producing Escherichia coli on pork carcasses for three steps of the harvest process at two commercial processing plants in the United States

Authors: NASTASIJEVIC, IVAN - Institute Of Meat Hygiene And Technology; Schmidt, John; BOSKOVIC, MARIJA - University Of Belgrade; GLISIC, MILICA - University Of Belgrade; Kalchayanand, Norasak - Nor; Shackelford, Steven; Wheeler, Tommy; KOOHMARAIE, MOHAMMAD - Institute Of Environmental Health Laboratories And Consulting Group; Bosilevac, Joseph - Mick

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/2020
Publication Date: 12/17/2020
Citation: Nastasijevic, I., Schmidt, J.W., Boskovic, M., Glisic, M., Kalchayanand, N., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M., Bosilevac, J.M. 2020. Seasonal prevalence of Shiga toxin-producing Escherichia coli on pork carcasses for three steps of the harvest process at two commercial processing plants in the United States. Applied and Environmental Microbiology. 87(1):e01711-20. https://doi.org/10.1128/AEM.01711-20.
DOI: https://doi.org/10.1128/AEM.01711-20

Interpretive Summary: Escherichia coli that make Shiga toxin (STEC) are a food safety threat in beef. Unlike beef processors, pork processors do not conduct their own testing of products for STEC. The presence of STEC throughout pork processing is not well known, so we tested pork carcasses each season at 2 pork processing plants. STEC were lower in the winter, but still high on pigs coming into the processing plant regardless of season. The carcass scalding process and other interventions reduced STEC significantly. However, we were able to isolate and identify types of STEC that cause beef recalls on the pork carcasses. So based on this limited sampling, pork processors may need to consider STEC a potential contaminate.

Technical Abstract: Shiga toxin-producing Escherichia coli (STEC) is a foodborne pathogen that has a significant impact on public health, with strains possessing the attachment factor intimin referred to as enterohemorrhagic E. coli (EHEC) and associated with life-threatening illnesses. Cattle and beef are considered typical sources of STEC, but their presence in pork products is a growing concern. Therefore, carcasses (n=1,536) at two U.S. pork processors were sampled once per season at three stages of harvest (poststunning skins, postscald carcasses, and chilled carcasses) and then examined using PCR for Shiga toxin genes (stx), intimin genes (eae), aerobic plate count (APC), and Enterobacteriaceae counts (EBC). The prevalence of stx on skins, postscald, and chilled carcasses was 85.3, 17.5, and 5.4%, respectively, with 82.3, 7.8, and 1.7% of swabs, respectively, having stx and eae present. All stx-positive samples were subjected to culture isolation that resulted in 368 STEC and 46 EHEC isolates. The most frequently identified STEC were serogroups O121, O8, and O91 (63, 6.7, and 6.0% of total STEC, respectively). The most frequently isolated EHEC was serotype O157:H7 (63% of total EHEC). Results showed that scalding significantly reduced (P<0.05) carcass APC and EBC by 3.00- and 2.50-log10 CFU/100 cm2, respectively. A seasonal effect was observed, with STEC prevalence lower (P<0.05) in winter. The data from this study show significant (P<0.05) reduction in the incidence of STEC (stx) from 85.3% to 5.4% and of EHEC (stx plus eae) from 82.3% to 1.7% within the slaughter-to-chilling continuum, respectively, and that potential EHEC can be confirmed present throughout using culture isolation.