Distribution of Extremely Heat-Resistant Escherichia coli in the Beef Production and Processing Continuum.

Understanding the dynamics of stress-resistant Escherichia coli (E. coli) across the meat production and processing continuum is important for tracking sources of such microbes and devising effective modes of control. The Locus of Heat Resistance (LHR) is a ∼14-19 Kb genetic element imparting extreme heat resistance (XHR) in Enterobacteriaceae. It has been hypothesized that thermal and antimicrobial interventions applied during meat processing may select for LHRE. coli. Thus, our goal was to study the prevalence and molecular biology of LHRE. coli among lots of beef cattle (n = 3) from production through processing. Two hundred thirty-two generic E. coli isolated from the same animals through seven stages of the beef processing continuum (cattle in feedyards to packaged strip loins) were examined. LHRE. coli were rare (0.6%; 1 of 180) among the early stages of the beef continuum (feces and hides at feedlot, feces and hides at harvest, and preevisceration carcasses), whereas the prevalence of LHRE. coli on final carcasses and strip loins was remarkably higher. Half (14 of 28) of the final carcass E. coli possessed the LHR, while 79.2% (19 of 24) of the strip loin E. coli did. Eighty-five percent (29 of 34) of the LHRE. coli presented with the XHR phenotype. The selection or enrichment of LHRE. coli from harvest steps to the final products appeared unlikely as the LHRE. coli isolates were effectively controlled by antimicrobial interventions typically used during beef processing. Further, whole-genome sequencing of the isolates suggested LHRE. coli are persisting in the chilled processing environment and that horizontal LHR transfer among E. coli isolates may take place.