OBJECTIVETo determine the quantity of Streptococcus mutans (S. mutans) and the ratio of S. mutans to total bacteria in the dental plaque of different caries-susceptible children.

METHODSDental plaque samples from 26 children aged 3 years old to 4 years old were collected. The quantities of S. mutans and total bacteria were determined by TaqMan real-time fluorescence quantitative polymerase chain reaction (PCR). The ratio ofS. mutans to total bacteria in children with and without caries was calculated and statistically analyzed.

RESULTSIn children with and without caries, the quantities of S. mutans were 1.33 x 10(5) and 1.16 x 10(3) CFU x mg(-1), the total bacteria were 7.17 x 10(7) and 1.01 x 10(8) CFU x mg(-1), and the ratios of S. mutans to total bacteria were 0.058 6 and 0.018 6, respectively. Significant differences were observed in the quantities of S. mutans and the total bacteria as well as in the ratios of S. mutans to total bacteria of the two groups (P = 0.033, 0.418, 0.008).

CONCLUSIONThe quantities of total bacteria of the two groups show negligible difference. However, the quantity of S. mutans and the ratio of S. mutans to total bacteria in caries-susceptible children are higher than those in caries-free children. Therefore, the ratios of S. mutans to total bacteria in plaque are closely associated with the prevalence of dental caries in children.