Tolerance variations and mechanisms of Salmonella enterica serovar Newport in response to long-term hypertonic stress

Curing is a widely used food processing technology. However, the hypertonic stress in curing can induce varying degrees of resistance in foodborne pathogens, posing a potential threat to food safety. In this work, various Salmonella enterica serovar Newport (S. Newport) strains were cultured using 5% and 10% NaCl solutions (hypertonic stress), and the most sensitive and tolerant strains were selected using Weibull model to investigate the mechanism underlying the tolerance differences. With hypertonic-stress time prolonging, the leakage of nucleic acids and proteins of S. Newport were increased gradually, and the membrane potential of S. Newport declined after an increase. Compared with the sensitive strain, the tolerant counterpart exhibited the ability to maintain the integrity of cell membrane and sustain a high membrane potential level. The expression levels of upstream genes proV and otsB in the tolerant strain were significantly lower than those in the sensitive strain; but the Kdp and Trk systems and downstream genes proX, proW and otsA much highly expressed in the tolerant strain compared with the sensitive strain, leading to higher concentrations of intracellular K+ and trehalose, enabling better survival in hypertonic environment. The findings of this work offer valuable insights into pathogen survival mechanisms under hypertonic stress and contribute to the development of strategies for mitigating microbiological risks during long-term processing and storge in the cured food industry.