变异链球菌（变链菌）表面蛋白Pac对其与牙面的初始粘附起关键作用。以往对变链菌标准株研究提示srtA 基因存在多态性并可影响表面蛋白Pac介导的粘附力。我们前期小样本研究发现儿童牙菌斑变链菌srtA基因存在多个突变位点，但其在不同龋易感人群的分布尚不明了。为进一步探讨变链菌srtA基因多态性与龋易感性的关系，并揭示其对变链菌致龋性的影响，本课题拟进行大样本分子流行病学研究，对重症婴幼儿龋(S-ECC)和无龋儿童牙菌斑变链菌进行srtA基因全长双向测序，分析各突变类型在两组儿童的分布差异，并采用western blotting、放射性同位素标记及激光共聚焦技术分别检测变链菌表面蛋白Pac、对唾液包被羟基磷灰石颗粒的粘附力及所形成生物膜的特点，比较不同突变类型的srtA基因对这些指标的影响。筛选出与S-ECC易感相关的srtA基因突变类型，为寻找龋病预测及预防新靶标提供实验依据。

The cell surface protein antigen c (Pac) of streptococcus mutans (S. mutans) plays a vital role in bacterial initial adherence. It was reported that the polymorphisms of srtA gene of standard strain of S. mutans could influnce the adhension ability via Pac. In our recent study with a small sample, we found that srtA genes of S. mutans from the dental plaque of children showed a number of mutation sites. However, the distribution of the mutation in children with different caries susceptibility is still unknown. Therefore, we plan to conduct a large sample molecular epidemiology study to reveal the relationship betweeen the polymorphisms of srtA gene and caries susceptibility, and explore the inflence of mutation of srtA gene on the cariogenicity of S. mutans. We will detect the srtA gene of S. mutans isolates from severe early childhood caries (S-ECC) and caries-free children by DNA sequencing at both directions and compare the distribution of different mutation types in the two groups. Furthermore, Pac of S. mutans in different types of mutation will be detected by western blotting method. Adhension to saliva-coated hydroxylapatite will be evaluated by 3H-TDR radioiodination, and the charateristic of biofilm be observed by confocal laser scanning microscope. In sum, mutation types of srtA gene possibly related to S-ECC susceptibility will be screened, and they could become future targets for the prediction and prevention of dental caries.