Effect of Pre‐exposure to Sodium Chloride on the Resistance of Pathogens to Thermal and Acid Stresses

This study determined the effects of pre‐exposures to sodium chloride (NaCl) on the survival of three pathogens (Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes) when the organisms were subsequently treated with moderate heat (55C) or an organic acid (acetic acid). Pre‐exposure to 5% NaCl especially increased the thermal resistance of E. coli O157:H7 and L. monocytogenes, whereas there was no significant increase in thermal resistance for S. Typhimurium. Pre‐exposure to 10% NaCl reduced the resistance of the three pathogens to 1% acetic acid, and similar reductions in acidic resistance were observed in S. Typhimurium and L. monocytogenes samples that were pre‐exposed to 5% NaCl. These results indicate that prior exposure to NaCl can affect the resistance of pathogens to environmental stresses. PRACTICAL APPLICATIONS Subsequent stress responses of pathogens by stress‐adaptation should be addressed to develop the effective techniques for controlling pathogens in foods and environment. It is because that environmental stresses can provide varying results as some bacteria may become more resistant or even more virulent under such circumstances through stress reactions. Although salt does not have great effectiveness to inactivate populations of pathogens, it could affect the stress reactions of pathogens or the antimicrobial action of other preservation hurdles. In fact, the result of this study showed that pre‐exposure to NaCl resulted in difference stress responses of pathogens depending on the type of environmental stress subsequently applied. Therefore, this report could provide important information for developing control or preservative methods to improve the microbial safety of foods.