Relationship between the genetic polymorphisms of <italic>vicR</italic> and <italic>vicK Streptococcus mutans</italic> genes and early childhood caries in two-year-old children.

Background: The VicRK two-component signalling system regulates virulence and cariogenicity in <italic>Streptococcus mutans</italic> (<italic>S. mutans</italic>). The purpose of this study was to explore the genetic polymorphisms of the <italic>vicR</italic> and <italic>vicK</italic> genes, which are associated with dental caries in children with <italic>S. mutans</italic>. Methods: In this study, 121 (from each group) clinical <italic>S. mutans</italic> strains were isolated from caries-free children and children with high-severity caries to sequence the <italic>vicR</italic> and <italic>vicK</italic> genes. Genomic DNA was extracted from <italic>S. mutans</italic> strains and amplified using PCR. The PCR products were purified and sequenced. A chi-squared test and ABI Variant Reporter software were used to analyse the sequencing results. Results: The 242 clinically isolated <italic>S. mutans</italic> strains contained the full-length <italic>vicR</italic> and <italic>vicK</italic> genes. No nucleotide sequence insertions or deletions were observed in the two genes. Four silent point mutations were identified in the <italic>vicR</italic> genes, and no missense mutations could be detected. Forty-one mutations were identified in the <italic>vicK</italic> genes. In addition to 32 silent mutations, 9 missense mutations at the 173, 337, 470, 1051, 1132, 1258, 1260, 1277, and 1348 bp positions were found. The distribution frequencies of the missense mutations were not significantly different between the groups, except for the C470T mutation. The frequency of the C470T missense mutation was higher in the high-severity caries group than in the caries-free group. Conclusions: <italic>vicR</italic> sequences are highly conserved in <italic>S. mutans</italic> clinical isolates. The locus 470 missense mutation of the <italic>vicK</italic> gene may be related to caries in children with <italic>S. mutans.</italic> [ABSTRACT FROM AUTHOR]