Colonization of teeth in humans by Streptococcus mutans as related to its concentration in saliva and host age

The relationship of the salivary concentration of Streptococcus mutans and host age to the colonization of this organism on erupting teeth was studied in humans. Plaques were obtained from fissures and buccal surfaces of erupting permanent first and second molars of children 6 to 7 and 11 to 14 years old, respectively. In subjects of both age groups with salivary S. mutans concentrations below 5 x 10(2) colony-forming units per ml, the organism was detected on only a few of the tooth surfaces; at concentrations of 5 x 10(2) to 4.9 x 10(4) colony-forming units per ml more than half of the surfaces and at concentrations of 5 x 10(4) colony-forming units per ml or higher most of the surfaces were colonized by S. mutans. The frequency of detection and concentration of S. mutans in plaque as well as its concentration in saliva were higher in the case of the older children. However, when younger and older children with similar salivary S. mutans concentrations were compared, S. mutans was more frequently isolated from plaque from older children only in the case of children with below 5 x 10(2) colony-forming units per ml of saliva. Eleven of the 64 children studied had low or undetectable S. mutans levels in plaque and saliva. The salivary S. mutans levels of the parents of these children were lower than those of parents of a group of children with normal oral S. mutans levels.