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

Abstract

Background: 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.
Materials and Methods: 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.
Results: 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.
Conclusion: 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.
Key Words: Biofilm, biosurfactant, genes, Lactobacillus rhamnosus, Streptococcus mutans