Genotypic diversity and acidogenic potential of Streptococcus mutans genotypes isolated from in situ biofilms formed under strong cariogenic challenge in the presence of fluoride

This study evaluated the effect of fluoride (F) on genotypic diversity and acidogenic potential of Streptococcus mutans isolated from in situ dental biofilms under strong cariogenic challenge. In a cross-over in situ study, volunteers wore palatal appliances containing dentin slabs subjected to biofilm accumulation and sucrose exposure 8x/day. They were assigned to the following treatments: placebo dentifrice (PD), 1100 F dentifrice (FD), APF (acidulated phosphate fluoride) + PD, and APF+FD. At the end of each phase, biofilms were collected, bacteria counted, and S. mutans colonies were isolated, and their DNA extracted, followed by AP-PCR with the arbitrary primer OPA-02. Additionally, genotypes were assessed regarding their acidogenic potential. 128 S. mutans isolates (based on species-specific PCR) were obtained from clinical samples. AP-PCR identified 17 different genotypes, and at least one unique genotype was found irrespective of the tested conditions for most volunteers. No differences were observed in acidogenicity of genotypes among the treatments. Both genotypic diversity and acidogenic potential of S. mutans seem more related to exposure to a strong cariogenic challenge and individual characteristics than to F itself. • Fluoride did not alter S. mutans genotypic diversity in in situ biofilms. • 17 genotypes identified across 128 isolates under strong cariogenic challenge. • Acidogenic potential of S. mutans linked to individual traits, not fluoride use. • Crossover in situ model standardized sucrose challenge for controlled comparison.