Genotypic and phenotypic characterization of Streptococcus mutans isolated from dental caries

Streptococcus mutans, considered as principal causative agent of dental caries, maintains a biofilm lifestyle in the dental plaque. The oral cavity harbors numerous S. mutans strains, which displayed remarkable genotypic and phenotypic diversity. This study evaluated the genotypic and phenotypic diversity of 209 S. mutans strains isolated from 336 patients with dental caries and compared with the universal reference strain UA159. Our study has revealed a high degree of genotypic and phenotypic variability among the clinical strains. We observed significant differences in colony morphology, generation time, biofilm formation, bacteriocin and acid production while growing in culture medium. All the clinical isolates were able to lower pH while growing in THY broth. In consistent with phenotypic variations, we also observed tremendous level of genotypic variation by AP-PCR and gene specific PCR. AP-PCR analysis suggested that most of the patients with dental caries have distinct type of S. mutans strains. Genes related to various two component systems were highly conserved among the strains, however, bacteriocin encoding genes such as nlmAB, nlmC were absent in half of the clinical isolates. In sum, our study highlights the genotypic and phenotypic diversity of S. mutans clinical isolates and indicates the presence of diverse mechanism to initiate and establish the biofilm lifestyle which leads to tooth decay.