Genotypic and phenotypic analysis of Streptococcus mutans from different oral cavity sites of caries-free and caries-active children

Introduction: Streptococcus mutans exhibits extensive genotypic diversity, but the role of this variation is poorly understood. This study aimed to determine the number and distribution of genotypes of S. mutans isolated from caries‐active and caries‐free children and to evaluate some of their phenotypic traits. Methods: Stimulated saliva, tongue surface and biofilms over sound and carious teeth surfaces were sampled from 10 caries‐free and 11 caries‐active children aged 5–8 years. A total of 339 isolates of S. mutans were genotyped by arbitrarily primed polymerase chain reaction using OPA2 primer. One isolate from each genotype was tested for its acid susceptibility and its ability to form a biofilm. Results: Fifty‐one distinct genotypes were determined, one to three genotypes in each oral sample. A single genotype was detected in seven children, whereas the remaining 14 children exhibited two to seven genotypes. There were no significant differences in the number of genotypes detected in caries‐free and caries‐active children. No correlation was observed between the number of genotypes and the mutans streptococci salivary levels. Five of the six high biofilm‐forming genotypes were obtained from caries‐active children, although the differences in biofilm formation between isolates from caries‐free and caries‐active children were not statistically significant. Genotypes with low susceptibility to acid challenge were statistically more frequent among isolates from caries‐active children than among those from caries‐free children. Conclusion: The present data suggested that there were differences in the distribution of genotypes of S. mutans according to the oral site and that S. mutans populations differ in their acid susceptibility and ability to form biofilms, factors allowing their colonization of sucrose‐rich environments.