OBJECTIVETo analyze horizontal transmission patterns of Streptococcus mutans among caries-active preschool children for early interventions of dental caries.

METHODSPlaque samples obtained from 20 caries-active preschool children between 4 and 5 years of age were cultured under anaerobic conditions for isolating S. mutans, which were identified by morphological and biochemical analyses and PCR using primers homologous to the surface protein glucosyltransferase B (gtfB). The genotypes of the isolated S. mutans strains were determined by arbitrarily primed PCR (AP-PCR).

RESULTSOf the 200 S. mutans isolates obtained, 19 were excluded by biochemical analysis, and the remaining 181 isolates were identified as S. mutans by PCR with primers of gtfB, showing 37 different genotypes as identified by AP-PCR. Six children were found to carry S. mutans of a single genotype, 11 carried 2 genotypes, 2 had 3 genotypes, and 1 had 4 genotypes; 2 children from different classes were found to carry S. mutans of the same single genotype.

CONCLUSIONWe identified 37 genotypes of S. mutans in these caries-active preschool children, among whom horizontal transmissions of the strains were not found.