Influence of Ethanol Adaptation on Salmonella enterica Serovar Enteritidis Survival in Acidified Media and Selected Fruit Juices

Introduction: Salmonella enterica serovar Enteritidis can encounter mild ethanol stress during its life cycle. Adaptation to the stress may later protect bacteria against heterogeneous stresses, thus counteracting the effectiveness of currently employed food control measures.

Purpose: This work was undertaken to evaluate the ability of Salmonella Enteritidis to develop acid resistance following ethanol adaptation.

Methods: Salmonella Enteritidis was subjected to ethanol adaptation in 5% ethanol for 1 hour. The tolerance of ethanol-adapted Salmonella Enteritidis to acetic, ascorbic, lactic, citric, malic and hydrochloric acids was assessed by the modulation of minimum inhibitory concentration and minimum bactericidal concentration values. The survival rates of non-adapted and ethanol-adapted Salmonella Enteritidis in refrigerated (4°C) and room temperature (25°C) stored apple juice and orange juice were also compared.

Results: Ethanol-adapted Salmonella Enteritidis only mounted cross-tolerance to one of the six acids tested, namely, malic acid. The survival of Salmonella Enteritidis in orange juice was not significantly (P>0.05) influenced by ethanol adaptation. However, an increased tolerance was noted with ethanol-adapted cells of Salmonella Enteritidis compared to non-adapted ones in apple juice stored at 25°C (P < 0.05), but not at 4°C.

Significance: These findings suggest the convenience to control the storage temperature as a strategy to prevent the development of cross-protection in acidic fruit juices. Furthermore, the combination of ethanol and malic acid applied sequentially should be avoided in food-related environments.