Antimicrobial and Antibiofilm Activity of a Lactobacillus reuteri SGL01, Vitamin C and Acerola Probiotic Formulation Against Streptococcus mutans DSM20523

Dental caries is a multifactorial chronic infectious disease that impacts healthcare costs globally, caused by alterations of the plaque microbiome and proliferation of cariogenic <i>Streptococcus mutans</i>. Treatments targeting <i>S. mutans</i>, such as alternative strategies using probiotics, might be effective in preventing the development of dental caries. In this study, the probiotic formulation of <i>Lactobacillus reuteri</i> SGL01, vitamin C, and acerola was tested against <i>S. mutans</i> DSM20523. Antimicrobial activity was assessed by deferred antagonism and spot-on-lawn assays for <i>L. reuteri</i> SGL01. MIC and MBC of <i>L. reuteri</i> SGL01 cell-free supernatant (CFS), vitamin C, and acerola were determined with the microdilution method. Time-kill assays determined the bactericidal kinetics for each compound. The checkerboard method was used to evaluate the potential synergistic activity of CFS-vitamin C or CFS-acerola at scalar dilutions from 1 to 8X MIC. Lastly, antibiofilm activity was tested for each compound. Antimicrobial activity of <i>L. reuteri</i> SGL01 was first assessed by classic methods. MIC and MBC values differed for one dilution for all compounds, with values of 25% and 50% for CFS, 9.3 mg/mL and 18.7 mg/mL for vitamin C, and 18.7 mg/mL and 37.5 mg/mL for acerola, respectively. Moreover, time-kill assays confirmed the bactericidal activity at different timepoints: 4 h for CFS, 6 h for vitamin C, and 24 h for acerola. The fractional inhibitory concentration index (FICI) showed indifference for all combinations, and for associations tested at 2, 4, and 8XMIC. <i>S. mutans</i> biofilm production was impaired for all components, with stronger activity by vitamin C and acerola at lower concentrations. The probiotic formulation containing <i>L. reuteri</i> SGl01, vitamin C, and acerola extract exerts a bactericidal effect, especially strong for the CFS, as well as antibiofilm activity. Thus, the combination of these three components could be advantageous for their complementary effects, with use as a novel treatment against the development of dental caries by <i>S. mutans</i>.