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

Objectives To assess the variations in hypertonic tolerance among Salmonella enterica serovar Newport (S. Newport) strains isolated from diverse sources and investigate the mechanism underlying the tolerance differences between the sensitive and tolerant strain.Materials and Methods In this work, various S. Newport strains were cultured in 5% and 10% NaCl solutions (hypertonic stress), and the most sensitive and tolerant strains were selected using a Weibull model. The regulatory mechanisms underlying the hypertonic tolerance differences of S. Newport were preliminarily investigated in the aspects of cell phenotype, intracellular solute concentration, and gene expression level.Results With prolonged hypertonic stress time, the leakage of nucleic acids and proteins of S. Newport increased gradually, and the membrane potential of S. Newport declined after increasing. Compared with the sensitive strain, the tolerant counterpart exhibited the ability to maintain the integrity of the cell membrane and sustain a high membrane potential level. The expression levels of the 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 were highly expressed in the tolerant strain compared with the sensitive strain, leading to higher concentrations of intracellular K+ and trehalose, enabling better survival in a hypertonic environment.Conclusions 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 storage in the cured food industry. Schematic diagram of the mechanisms underlying S. Newport hypertonic tolerance. ->: upregulation; ->: transport; ->: biosynthesis.