Lactobacillus rhamnosus biosurfactant inhibits biofilm formation and gene expression of caries‑inducing Streptococcus mutans

It is cleared that some probiotic strains inhibit biofilm formation of oral bacteria, but its mechanisms are not clearly understood yet. It is proposed that one of the mechanisms can be biosurfactant production, a structurally diverse group of surface‑active compounds synthesized by microorganisms. Hence, this study focused on the evaluation of the anti‑biofilm and antiadhesive activities of the L. rhamnosus derived‑biosurfactant against Streptococcus mutans and its effect on gtfB/C and ftf genes expression level. In this in vitro study Lactobacillus rhamnosus ATCC7469 overnight culture was used for biosurfactant production. The biosurfactant effect on the surface tension reduction was confirmed by drop collapse method. Chemical bonds in the biosurfactant were identified by Fourier transform infrared (FTIR). Anti‑biofilm and antiadhesive activities of the biosurfactant were determined on glass slides and in 96-well culture plates, respectively. The effect of the biosurfactant on gtfB/C and ftf genes expression level was also investigated after biofilm formation, total RNA extraction, and reverse transcription by quantitative real‑time reverse transcriptase polymerase chain reaction (PCR) assay (quantitative PCR). The data were assessed by one‑way analysis of variance in the Tukey–Kramer postdeviation test for all pairs. P < 0.05 was considered statistically significant. The FTIR results of biosurfactant showed that it was protein rich. It also showed anti‑biofilm formation activity on the glass slide and antiadhesive activity till 40% on microtiter plate wells. It also showed a significant reduction (P < 0.05) in gtfB/C and ftf genes expression level. L. rhamnosus‑derived biosurfactant exhibits a significant inhibitory effect on biofilm formation ability of S. mutans due to downregulation of biofilm formation associated genes, gtfB/C and ftf. L. rhamnosus‑derived biosurfactant with substantial antiadhesive activity is suitable candidates for use in new generations of microbial antiadhesive agents.