Antimicrobial effect of spore-forming probiotics Bacillus laterosporus and Bacillus megaterium against Listeria monocytogenes.

There are several reports on the detection of Listeria monocytogenes in Iran, which has been identified as a major public health problem. In addition, due to drug resistance and strong biofilm formation of this pathogen, new approaches such as using probiotics are needed to combat this bacterium. The aim of this study was to investigate the effect of spore-forming probiotics on the expression of virulence genes hly, plc, inlA, and invasion of L. monocytogenes. Spore-forming probiotics were co-cultured with L. monocytogenes at different time points and following cell count, the expression level of virulence genes of L. monocytogenes was assessed by real-time PCR. To investigate the effect of the isolated strains on the invasiveness of L. monocytogenes at different time points, HT-29 cell line was used. Sporulated probiotics reduced the growth of L. monocytogenes in broth medium at different time periods. The number of L. monocytogenes co-cultured with Bacillus laterosporus decreased by 1, 3, 3, and 6 log at 2, 4, 8 and 24 h after treatment, respectively. In addition, the expression of virulence genes was decreased at different time points and the expression of hly and plcA genes was more affected. The invasion rate of L. monocytogenes on HT-29 cells was decreased by 1 to 6 log at different time points. Both probiotic strains inhibited bacterial growth at different time points; however, more sensitive methods should be established for an accurate assessment.