Purpose: The aim of this study was to determine the heat and pressure resistance of a large group of VTEC and compare them to E. coli AW1.7, an extremely heat and pressure resistant beef isolate.
Methods: Eighty-seven strains of VTEC and fifteen verotoxin-negative E. coli representing 15 different serotypes were screened for survival of thermal treatment at 60°C for 5 min in LB broth. Nineteen heat resistant and sensitive strains were pressure treated at 600 MPa and 25°C for 3 min in LB broth. Pressure treatment was applied to ground beef inoculated with the 4 most pressure resistant strains of E. coli.
Results: With an initial concentration of 7 log CFU/ml, 77 of the 102 strains tested did not have survivors following 60°C for 5 min. Of the 25 heat resistant strains, 6 strains of VTEC were reduced by 4.2 log CFU/ml or less. Eight of the pressure treated strains were reduced by less than 2 log CFU/ml in LB broth. In ground beef the most pressure resistant VTEC was E. coli O26:H11 05-6544 with a reduction of 2.0 ± 0.1 log CFU/g; E. coli AW1.7 was reduced by 2.9 ± 0.8 log CFU/g.
Significance: The results of these experiments demonstrate that E. coli AW1.7 is more heat resistant than the VTEC strains tested. A number of the VTEC were resistant to pressure and survived treatment that is equivalent to current commercial processes (600 MPa at ambient temperature).