Variation in heat and pressure resistance of verotoxigenic and nontoxigenic Escherichia coli.

This study evaluated the heat and pressure resistance of 112 strains of Escherichia coli, including 102 strains of verotoxigenic E. coli (VTEC) representing 23 serotypes and four phylogenetic groups. In an initial screening, the heat and pressure resistance of 100 strains, including 94 VTEC strains, were tested in phosphate-buffered saline (PBS). Treatment at 60°C for 5 min reduced cell counts by 2.0 to 5.5 log CFU/ml; treatment at 600 MPa for 3 min at 25°C reduced the cell counts by 1.1 to 5.5 log CFU/ml. Heat or pressure resistance did not correlate to the phylogenetic group or the serotype. A smaller group of E. coli strains was evaluated for heat and pressure resistance in Luria-Bertani (LB) broth. Generally, the levels of heat resistance of E. coli strains in LB and PBS were similar; however, the levels of pressure resistance observed for treatments in LB broth or PBS were variable. The cell counts of pressure-resistant strains of VTEC were reduced by less than 1.5 log CFU/ml after treatment at 600 M...