Genotypic diversity of Streptococcus mutans in 3- to 4-year-old Chinese nursery children suggests horizontal transmission

OBJECTIVE: The aims of this study were to investigate the colonisation of Streptococcus mutans and to determine the possibility of horizontal transmission in Chinese nursery children. DESIGN: Fifty-six children aged between 3 and 4 years old from a nursery were included in this study. Twenty-four children were from the day and night nursery class, the others were from the day nursery class. Dental plaque samples were collected with sterile toothpicks and cultured on S. mutans-selective tryptone-yeast-cystine agar supplemented with 0.2U/ml bacitracin and 15% sucrose. The typical isolates of S. mutans were identified by classical microbiological methods and genotyped by arbitrarily primed PCR (AP-PCR) and restriction fragment length polymorphism analysis. RESULTS: S. mutans was isolated from 41 of the 56 children. The prevalence of S. mutans was higher in the children from day nursery class, compared with the children from day and night nursery class (P<0.05). A total of 140 S. mutans isolates from 41 children were analysed by AP-PCR, and 88 different amplitypes were identified. Of 41 children with S. mutans isolates, 82.9% carried two or more genotypes. Two genotypes of S. mutans were repeatedly isolated among 13 children in the day and night nursery class, and one genotype was isolated from two children in the day nursery class. CONCLUSION: The presence of matching genotypes of S. mutans among children attending the same nursery suggests the possibility of horizontal transmission.