Objectives: We have previously shown that caries-active children in Head Start Programs in Iowa have more S. mutans clonal types than caries-free children. However, these studies were cross-sectional only. The purpose of this study was to delineate SM clonal type profiles in these young children over time. Methods: We have established a cryolibrary of 10 SM isolates per subject from Head Start Program children taken at different periods of time. For our initial analyses, DNA was extracted from 10 isolates per subject from caries-active and caries-free children at each of these timepoints: baseline, 3 months, and 6 months. Arbitrarily-primed polymerase chain reaction (AP-PCR) was performed as described by Li (Li and Caufield, 1998) with some modifications. Amplification was performed with the following temperature profile: initially 5 minutes at 94⁰C, followed by 45 cycles of 1 minute at 94⁰C (denaturation), 1 minute at 36⁰C (annealing), and 2 minutes at 72⁰C (elongation). Amplification mixture (master mix) consisted of: DNAase free H2O, 10X amplification buffer, dNTP (0.2 mM), MgCl2 (7uM), Primers OPA-2 and OPA-13 in separate runs, and Taq Polymerase. Results: Children at baseline exhibited 1-2 SM clones only. At 3 months, a much more diverse and complex profile of SM clones emerged, with subjects exhibiting 4-5 clonal types. Some were new and not seen in the children at baseline. By 6 months, the SM clonal type profiles had changed dramatically with the loss of some new clones, but establishment of others. Overall, the SM profiles had become less complex, with only 1-2 clones per subject. Conclusion: Our data suggest that the clonal type profiles of S. mutans in 3-year-old caries-active children appear to be dynamic and complex. Our current studies are focusing on comparisons of SM clonal types and virulence in caries-free versus caries-active children. Supported by NIH/NIDCR T32-DEO-14678

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