Postbiotic-mediated antibiofilm activities of newly isolated LAB strains against cariogenic pathogens

Postbiotics, the metabolites from probiotics, offer a promising approach for controlling oral biofilms through the inhibition of adhesion, degradation of established biofilms, or by exerting antimicrobial effects. This study evaluated the antibiofilm properties of the cell-free supernatants (CFS) of newly isolated Lactiplantibacillus plantarum GS2 and Pediococcus pentosaceus BM1 against cariogenic pathogens Streptococcus mutans and Streptococcus oralis. The antibiofilm activity of concentrated CFS was found to be mediated by heat-stable, protease-resistant bioactive metabolites. pH neutralization of concentrated CFS revealed the effect of non-acidic metabolites on antibiofilm activities. Among the probiotic characteristics, the GS2 strain exhibited higher DPPH scavenging activity (18.76%) and cell-surface hydrophobicity with hexadecane (44.52%), chloroform (63.06%), toluene (38.47%), and benzene (32.27%). Furthermore, both strains exhibited remarkable auto-aggregation and coaggregation properties with oral pathogens. Notably, CFS of GS2 and BM1 exhibited a loss of or weak antimicrobial activity against S. mutans and S. oralis upon pH neutralization, suggesting that the antimicrobial activity is mainly pH-dependent. Interestingly, CFS at their natural and neutralized pH significantly reduced the biomass of pre-formed biofilms (24 h) of S. mutans and S. oralis. In addition, the anti-adherence assay, performed by precoating CFS to the microtiter wells, revealed significant anti-adherence activities (30-40%) against oral pathogens irrespective of their pH. This activity likely indicates the presence of metabolites like biosurfactants that can interfere with surface-pathogen interactions. This study also demonstrated the biocompatibility of neutralized postbiotics in L929 and HGF cell lines, which might be useful for oral applications.