Antimicrobial effect of spore-forming probioticsBacillus laterosporusandBacillus megateriumagainstListeria monocytogenes

There are several reports on the detection ofListeria monocytogenesin 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 geneshly,plc,inlA, and invasion ofL. monocytogenes. Spore-forming probiotics were co-cultured withL. monocytogenesat different time points and following cell count, the expression level of virulence genes ofL. monocytogeneswas assessed by real-time PCR. To investigate the effect of the isolated strains on the invasiveness ofL. monocytogenesat different time points, HT-29 cell line was used. Sporulated probiotics reduced the growth ofL. monocytogenesin broth medium at different time periods. The number ofL. monocytogenesco-cultured withBacillus laterosporusdecreased 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 ofhlyandplcAgenes was more affected. The invasion rate ofL. monocytogeneson 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.