Abstract: Objective To analyze horizontal transmission patterns of Streptococcus mutans among caries-active preschool children
for early interventions of dental caries. Methods Plaque 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). Results Of 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. Conclusion We identified 37 genotypes of S. mutans in these caries-active
preschool children, among whom horizontal transmissions of the strains were not found.