Objective: The purpose of this study was to analyze the infra-specific variability and the cariogenic potential of Streptococcus mutans strains isolated from caries-free individuals (DMFT=0). Methods: Samples of three different sites (saliva, dental plaque and tongue surface) were collected using sterilized swabs. After dispersion and seriate dilution of the samples, aliquots from each dilution were inoculated in MSB agar plates and incubated under 10% CO₂ conditions (37ºC), mutans streptococci was counted, and 15 to 20 typical morphotype colonies, from each site, were isolated and subjected to biochemical typing and amplification by the technique of Polymerase Chain Reaction (PCR). Protein extracts obtained by cell disruption were separated by starch gel electrophoresis and specifically stained in order to obtain the isoenzymic polymorphism The gels were analyzed for five enzymatic systems: M1P, LAP, MPI, NSP e PLP. The cariogenic potential of these microorganisms was analyzed by the capacity of acid production in increasing intervals of time (0, 3, 6, 12 and 24 hours) and sucrose-dependent adherence in vitro. Results: The comparative analysis of MLEE profiles assessed by the sum of all enzymatic systems demonstrates the occurrence of one or more S. mutans clone within each different intra oral sites among these volunteers. Identical clonal type had similar cariogenic potential. In some volunteers different clones had difference in the capacity of acid production. Conclusions: The obtained results showed that it may be found more than one genetic type of S. mutans colonizing different sites in a same subject and this clones can have different cariogenic potential. Supported by FAPESP Proc. nº 99/05183-7; 99/09393-6.

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