Effect of Cell-Free Culture Supernatants (CFCS) of Lactic Acid Bacteria on Salmonella AI-II Activity and Biofilm Formation

In this study, we evaluated the cell-free culture filtrates (CFCS) from nine distinct species of lactic acid bacteria (M10: Lactococcus lactis subsp. cremoris, M13: Lactococcus lactis N8, M14: Lactococcus lactis LL3, M19: Lactobacillus plantarum, M20: Pediococcus acidilactici, M22: Lactobacillus rhomnousus NCDO1856, M23: Bifidobacterium longum CHL28, M24: Bifidobacterium bifidum CHL17, M36: Pediococcuspentosaceus FBB61.1) for biofilm formation and autoinducer (AI-II) activity in Salmonella Typhimurium strains DMC4 and SL1344, including their respective ΔluxS mutants. Applying 40% M24-coded CFCS to S. Typhimurium DMC4 resulted in a maximum biofilm inhibition of 83.02 ± 1.43%. Notably, the highest antibiofilm activity in the ΔluxS of this strain was observed using a 40% concentration of CFCS derived from the M10-coded LAB strain, achieving an inhibition rate of 94.64 ± 0.95%, and in the case of S. Typhimurium SL1344, the wild-type. Its ΔluxS mutant exhibited significant biofilm reductions of 79.12 ± 1.38% and 97.01 ± 2.36%, respectively, when treated with 40% M23-CFCS. Furthermore, it was determined that LAB-CFCS exerted a suppressive effect on AI-II activities, with the highest level of AI-II signal inhibition (90.91%) observed in the S. Typhimurium DMC4 wild-type, facilitated by CFCS from strains M10, M19, M20, M22, M24, and M36. In this study, significant effects of culture supernatants obtained from lactic acid bacteria on biofilm inhibition and AI-II activity on Salmonella Typhimurium strains were observed. In general, some lactic acid bacteria significantly inhibited biofilm formation in both strains. However, the results obtained suggest that lactic acid bacteria may potentially play an important role in pathogen control by enhancing antibiofilm activity on Salmonella strains.