Evaluation of the strain variability of Salmonella enterica acid and heat resistance.

The inherent acid and heat resistances of 60 Salmonella enterica strains were assessed in tryptone soy broth without dextrose acidified to pH 3.0 or heated at 57 °C. A total of 360 inactivation curves were generated. Regarding the acid challenge experiments, the inactivation rate (kacid), estimated using the log-linear model, ranged from 0.47 to 3.25 h(-1). A log-linear model with a "survival tail" was used to describe the thermal inactivation of the strains, and the estimated inactivation rate (kheat) ranged from 0.42 to 1.33 min(-1). The strain variability of kacid was considerably higher than that of kheat with the coefficient of variation of this kinetic parameter among the tested strains being 39.0% and 18.3%, respectively. No correlation was observed between the estimated kacid and kheat values of the 60 S. enterica strains. Furthermore, no trends among the tested strains related to origin, serotype or antibiotic resistance profile were evident. The present study is the first one to comparatively evaluate the inherent acid and heat resistance profiles of multiple S. enterica strains. Beyond their value in strain selection for use in food safety challenge studies, the collected data should be useful in describing and integrating the strain variability of S. enterica acid and heat resistance profiles in quantitative microbial risk assessment.