Anti-Bacterial and Anti-Biofilm Activities of Cell-Free Supernatant of Lactobacillus johnsonii Against Salmonella Typhimurium.

Salmonella Typhimurium is a predominant foodborne pathogen whose robust biofilm-forming capacity poses a persistent challenge to food safety and public health. This study investigated the inhibitory effects of cell-free supernatant (CFS) derived from Lactobacillus johnsonii on biofilms and characterized the transcriptional responses associated with CFS exposure using RNA sequencing (RNA-seq). L.johnsonii CFS retarded bacterial growth at high concentrations. Moreover, CFS at various concentrations significantly inhibited biofilm formation in both S. Typhimurium strains, SL1344 and 14028, with maximum inhibition rates of 88.22% and 79.32%, respectively. CFS treatment markedly reduced metabolic activity, surface hydrophobicity, and auto-aggregation, meanwhile impaired bacterial motility and disrupted the architectural integrity of the biofilms. Furthermore, the CFS effectively prevented biofilm formation on various food and food-contact surfaces. RNA-seq analysis revealed that CFS treatment significantly altered the transcriptional profiles of Salmonella, with differentially expressed genes mainly enriched in ribosome, carbon metabolism, oxidative phosphorylation, secondary metabolite biosynthesis, and microbial metabolism in diverse environments. These findings demonstrate the antibiofilm potential of L. johnsonii CFS under laboratory conditions and indicate its potential in controlling Salmonella contamination in food industry.