Characterization of Escherichia coli possessing the locus of heat resistance isolated from human cases of acute gastroenteritis

The purpose of this study was to identify Escherichia coli isolates obtained from patients experiencing acute gastroenteritis that possess the locus of heat resistance (LHR) and characterize their heat resistance upon exposure to temperatures of 60 degrees C and 71 degrees C. From a collection of 613 clinical E. coli strains, 3 heat resistant E. coli isolates were identified. Two of the 3 isolates were stx1 positive; no isolates possessed stx2 as determined by qPCR. D-60-values of heat resistant isolates all exceeded 10.20 min with one isolate's D-60-values ranging from 20.46 to 72.47 min. The presence of 4% additional NaCl significantly increased D-60-values of 2 clinical isolates. Cell reductions of heat resistant isolates in ground beef patties grilled to 60 degrees C and 71 degrees C remained above 2.8 and 4.9 log CFU/mL, respectively, compared to reductions of 6.1 log CFU/mL and greater in heat sensitive E. coli. Constitutive expression of novel Clp protease ClpK, encoded on open reading frame 3 of the LHR, was identified in all heat resistant isolates by SDS-PAGE and peptide mass fingerprinting. This data is the first to report heat resistant E. coli possessing the LHR involved in clinical infection, highlighting the potential threat of heat resistant enteric pathogens on food safety.