Heat Tolerance of Wildtype Salmonella Tennessee and Its Knock-Off Mutants in Peanut Butter and Peanut Spread

Salmonella enterica from low-moisture food has been found to have a higher thermal tolerance than from high-moisture food. However, the molecular mechanism underlying the association of thermal tolerance of this pathogen with low-moisture foods, such as peanut butter and peanut spread, has not been fully elucidated. We previously found that mutants of S. Tennessee with a defective gene encoding a cell membrane lipoprotein (Lpa) or cell division protein (ZapC) formed significantly (p ≤ 0.05) less biofilm than the wildtype strain. To assess the possible role of these genes in the thermal tolerance of S. Tennessee, this study compared the surviving populations of the wildtype S. Tennessee and its mutants defective in Lpa or ZapC in different types of peanut products (regular, reduced-fat, and natural) at 74 °C for 0, 2.5, 5, 10, 15, 20, 30, 40, or 50 min. Results showed that mutants with a defective lpa or zapC significantly affected the survival of Salmonella in peanut products during heat treatments. Significantly, a higher reduction in Salmonella population was observed in regular peanut butter, followed by natural and reduced-fat peanut spreads. The study provides new insight into one of the molecular mechanisms underlying the thermal tolerance of Salmonella enterica.