Diversity Assessment of Heat Resistance of Listeria monocytogenes Strains in a Continuous-Flow Heating System

Abstract

Listeria monocytogenes is a foodborne pathogen that has the ability to survive relatively high temperatures compared with other nonsporulating foodborne pathogens. This study was performed to determine whether L. monocytogenes strains with relatively high heat resistances are adequately inactivated in a high-temperature, short-time pasteurization process (72°C for 15 s). To obtain heat-resistant strains, 48 strains were exposed to 55°C for up to 3 h. The energy of activation constant and inactivation constant of strains that survived best (strains 1E and NV8) were subsequently determined in a continuous-flow-through system. Strain Scott A was taken along as a reference. The 3 strains were cultured in whole milk and in brain heart infusion broth at 30 and 7°C. Strains 1E and NV8 were significantly more heat resistant than was strain Scott A after growth in brain heart infusion broth at 30°C and after growth in milk at 7°C. From the inactivation parameters, it was calculated that exposure to high-temperature, short-time pasteurization (72°C for 15 s) will result in 12.1-, 14.2-, and 87.5-log reductions for the strains 1E, NV8, and Scott A, respectively. These results demonstrate that industrial pasteurization conditions suffice to inactivate the most heat-resistant L. monocytogenes strains tested in this study.