Lactic acid bacteria and Culture Media for the Production of Potential Antivirulence Peptides against Salmonella Typhimurium

In the current research, eleven strains of lactic acid bacteria (LAB) were screened for the production of bioactive peptides with antivirulence activity. Moreover, the effect of different nitrogen and carbon sources on the production of antivirulent peptides was investigated by employing the proteolytic system of Lactobacillus acidophilus La-5. A cell free spent medium (CFSM) was prepared from each phase of the research. Initially, a bioluminescence assay was conducted to test the antivirulence activity of these CFSMs against Salmonella Typhimurium (ssrB::luxCDABE and hilA::luxCDABE). A two-step RT-qPCR was conducted to confirm any effect of the CFSMs on the expression of these virulence genes. The greatest down-regulation of the virulence genes was observed in the presence of CFSMs from highly proteolytic LAB strains, while strains with less active proteolytic activity showed the lowest inhibition. The La 5 CFSM in Whey Protein Concentrate showed a significant suppression of the expression of the virulence genes.