Synergistic pairing of Lactobacillus helveticus Stellar Lh-170 and Lactiplantibacillus plantarum Stellar Lp-199 suppresses Streptococcus mutans and disrupts cariogenic biofilms

Background Streptococcus mutans exists within a biofilm ecosystem where neighboring microbes influence each other’s viability. Probiotic strains with complementary antagonistic properties may enhance suppression beyond individual strains. An evaluation of probiotic combinations assessed synergistic biofilm and pathogen suppression.Methods Nineteen probiotic strains were screened for hydrogen peroxide production and antagonism of Streptococcus mutans; five candidates were further tested in two-strain combinations for synergistic antagonism of S. mutans and hydroxyapatite adhesion. An artificial saliva culture model assessed both the inhibition and disruption of S. mutans biofilms alone and with Candida albicans, with findings validated on human molars.Results Of the 19 strains assessed, Lactobacillus helveticus StellarTM Lh-170 and Lactiplantibacillus plantarum StellarTM Lp-199 exhibited the strongest synergistic antagonism against all tested S. mutans strains (p < 0.001). Both strains rapidly produced H2O2 and adhered to hydroxyapatite. When co-incubated at a 10:1 ratio with S. mutans, the combination reduced biofilm biomass by 62% (n.s.) and significantly reduced S. mutans viability below detectable CFU limits (~107-fold reduction). When co-incubated with S. mutans and C. albicans together, dose-dependent reductions in the viability of both pathogens were observed. When pre-established S. mutans biofilms were treated with the two-strain combination, the number of viable S. mutans CFUs was reduced by > 10,000-fold in vitro and 3,135-fold in extracted human molars after 24 h (p < 0.0001).Conclusions Synergistic strain combinations effectively modulate cariogenic pathogens in vitro, exceeding benchmark strains. These findings support the clinical evaluation of the Lactobacillus helveticus Stellar Lh-170 and Lactiplantibacillus plantarum Stellar Lp-199 combination for prophylactic caries risk management.