Estudo longitudinal das vias potenciais de transmissão de Streptococcus mutans durante a colonização inicial de bebes de creches publicas da cidade de Piracicaba (São Paulo) / Longitudinal study of potential sources of transmission of Streptococcus mutans during the initial colonization of children from public nurseries in Piracicaba (São Paulo)

Alessandra Castro Alves

Children are more likely to acquire Streptococcus mutans in the oral cavity during the early years of their lives. The mothers are often the main source of S. mutans transmission. This study aimed to identify non-mother potential sources of S. mutans transmission in a population of nursery children during the period of initial colonization, using arbitrarily primed polymerase chain reaction (AP-PCR). 160 infants from 28 public nurseries schools of the city of Piracicaba (Brazil), with initial age between 5-13 months, were enrolled in this prospective study. Levels of S. mutans infection were determined during a 18-month follow-up period, in which children were examined at each 6-month period. Number of erupted teeth and caries were also analyzed. AP-PCR profiles of the children S. mutans isolates were also obtained with the amplitypes of the S. mutans strains that were isolated from their 61 respective day-care nurses. S. mutans isolates obtained from a subset of sixteen mothers whose children harbored high levels of S. mutans were also analyzed by AP-PCR. S. mutans strains were isolated from samples of saliva that were collected with tongue blades and inoculated onto MSB (Mitis Salivarius and Bacitracina). Plates were incubated at 37oC for 48 hours. The number of S. mutans-like colonies was determined using a stereoscopic microscope. Eight isolates of S. mutans per subject were picked up from each plate and pure cultures stored. Genomic DNA purified from the isolates were subjected to AP-PCR using OPA-02. PCR products were electrophoretically resolved in agarose gels. Comparisons of AP-PCR amplicon profiles were performed between children attending the same nursery, and between children and their respective nurse and/or mother by side-by-side visual comparison. Amplitypes were considered similar when all major bands were identical. The degree of similarity of a subset of visually matching strains were also analyzed with the help of the Fingerprinting II informatix software. S. mutans were isolated from children as young as 6 months of age. At baseline (T0), S. mutans were detected in 5.6% of the children. This prevalence increased to 15.6, 32.1 and 40.3% respectivelly at the subsequent follow-up periods (T6, T12, T18). The median age of initial acquisition was 21 months. Children harbored one to four distinct amplitypes. A subset of 16 children carried the same amplitype of their nursery mates in at least one of the phases of the study, suggesting child-child horizontal S. mutans transmission. Amplitype matching among mother-child pairs were detected in 50% of the subset analyzed indicating transmission from mothers to their children. Sixty-eight percent of the mothers were heavily infected. Mothers were colonized by one-four amplitypes. Although most of the nurses harbored high levels of S. mutans (51.5%), their S. mutans amplitypes did not match amplitypes detected in their respective children. Nursery children may be colonized by diverse S. mutans genotypes during the first two years of age in the studied population, and that children may acquire S. mutans by child-child horizontal transmission. That is compatible with the relative low prevalence of S. mutans amplitype matching among child-mother pairs

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