Increased D-Values for Salmonella enteritidis Following Heat Shock

Early stationary-phase cells of Salmonella enteritidis (ATCC 4931) were heat shocked at 42°C for 60 min. Following heat shock, the cells were transferred to casein soymeal peptone-yeast extract broth medium and experiments were conducted to generate survivor curves and D-values. Survivors were enumerated after heat shock under both aerobic and strict anaerobic conditions. Control cells were not stressed. Heat-shocked cells had significantly (P < 0.05) higher D-values than unstressed cells at 52, 54, and 56°C, but not at 58°C. Anaerobic enumeration further increased D-values, but not always to a significant extent. Heat shock resulted in the overexpression of seven proteins, detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This study suggests that (i) short-term temperature abuse of foods containing S. enteritidis may render these cells more resistant to subsequent heat treatments; (ii) anaerobic microenvironments may enhance survival of heat-stressed S. enteritidis ; and (iii) heat shock results in the overexpression of proteins that may be related to increased thermotolerance.