Time of initial acquisition of mutans streptococci by human infants.

The aim of this study was to detect and monitor the acquisition of mutans streptococci (MS) in healthy Brazilian children. Samples of 4 different sites (saliva, tongue dorsum, dental ridges, and dental plaque, if teeth were present) were collected from 33 edentulous nursery school infants (5.9+/-1.5 month-old), using sterilized swabs, bi-monthly for 24 months. Saliva samples from the mothers were collected only once. After inoculation, and incubation typical morphotype colonies, were isolated and submitted to amplification by the technique of polymerase chain reaction (PCR) for identification. The PCR method identified 1667 strains as MS In 29 of the children's samples, the first positive culture for MS occurred at 15.3+/-4.6 months. At the end of the follow-up period, 77% of the children were classified as colonized and in 33% MS was found as a transient microorganism. A positive correlation was found between the time of MS acquisition by the infant and the number of erupted teeth (p<0.0001), and the time of emergence of the first tooth (p=0.0048). After 24 months, there were no dental caries, and 77% of children remained caries-free. These results indicate that MS colonization in this sample of low-income pre-school children may begin earlier than suggested by some investigations.