Membrane damage effect and mechanism of sublethally injured Salmonella Typhimurium induced by lactic acid.

Salmonella is widespread in foods, which could survive in sublethally injured state during processing and preservation with various techniques. To further elucidate the membrane damage effect and mechanism of sublethally injured cells, the sublethal injury effects of lactic acid (LA) on S. Typhimurium in domestic wastewater and broth were studied. Meanwhile, membrane chemical composition, surface characteristics, and biological function were also analyzed, along with proteomics analysis, to clarify membrane damage mechanism. LA could induce cytoplasmic membrane (CM)-injured and outer membrane (OM)-injured S. Typhimurium. The membrane proteins of injured cells significantly decreased, accompanying augmented saturated fatty acids and declined unsaturated fatty acids, which indicated chemical composition of bacterial membrane remarkably altered. The cell morphology displayed obvious alterations, surface hydrophobicity and zeta potential of injured S. Typhimurium increased while average size decreased. Furthermore, the permeability of both CM and OM increased, the integrity of CM also compromised, which could cause abnormal biological function. Data-independent-acquisition based proteome revealed that the outer membrane proteins located in OM and the transporters in CM were affected obviously. Apart from identifying the sublethal injury effect of LA on Salmonella, this work also clarified the membrane damage mechanism of injured bacteria from cellular and molecular levels.