Horizontal Transmission of S. mutans Amplitypes in Brazilian Nursery Children

″Objectives:″This prospective study aimed to identify alternative sources of S. mutans transmission in nursery children during initial colonization using arbitrarily primed polymerase chain reaction (AP-PCR). ″Methods:″ 160 infants from public nurseries schools of Piracicaba (Brazil), with initial age between 5-13 months, were enrolled in this study to determine their initial infection by S. mutans and the colonization during 18 months. Clinical exams were performed to record the erupted teeth and caries. Their 60 respective day-care nurses and sixteen mothers whose children harbored high levels of S. mutans were also analyzed. Samples of saliva were collected with tongue blades and inoculated onto Rodac^® plates containing MSB (bacitracin). Plates were incubated at 37oC (48 hours) and the number of colonies was determined. Eight isolates/subject were picked up from each plate and stored at 70oC. The amplitypes were determined by AP-PCR (OPA-02) and analyzed electrophoretically. Amplitypes were considered similar when all major bands were identical. ″Results:″ S. mutans were isolated from children as young as 6 months of age. The median of initial acquisition was 21 months. The children showed 1-4 distinct amplitypes. Nineteen children attending the same nursery carried the same amplitype, but that did not match amplitypes from their nurses. Similar amplitypes of S. mutans strains occurred in 50% of the 16 mother-child pairs. Sixty-eight percents of the mothers were heavily infected. ″Conclusions:″ The study demonstrated a low degree of homology between S. mutans strains from mother and nursery children. These data indicate that children from this Brazilian population may be colonized by diverse S. mutans amplitypes during the first year of age, but no evidence of S. mutans transmission from nurses to children was identified. The presence of matching amplitypes of S. mutans among children attending in same nurseries suggests horizontal transmission.

FAPESP: 02/07156-1