Genetic polymorphisms of the sortase A gene and early childhood caries in two-year-old children

Abstract Objective To explore and compare the genetic polymorphisms of the sortase A (srtA) gene found in Streptococcus mutans ( S. mutans ) infecting two-year-old children suffering early childhood caries to those found in caries-free children through molecular identification methods. Methods Clinical S. mutans strains were isolated from the dental plaques of two-year-old children. Fifteen strains of S. mutans from the caries-active group and 15 strains of S. mutans from the caries-free group were collected. Genomic DNA was extracted from the S. mutans isolates. DNA fragments, including the srtA gene, were amplified by PCR. The PCR products were purified, sequenced and analyzed. A chi-square test and BioEdit software were used to analyze the sequencing results. Results All 30 clinically isolated S. mutans strains had a 741 base pair (bp) srtA gene. There were no nucleotide sequence insertions or deletions observed in the srtA genes. Twenty mutations were identified in the srtA genes that taken from the 30 clinical strains. There were 10 silent point mutations at the 78, 99, 150, 165, 186, 222, 249, 261, 312, and 636 bp positions. The other 10 mutations were point mutations resulting in a missense mutation at the 23, 34, 36, 47, 112, 114, 168, 176, 470, and 671 bp positions. None of the positions were enzyme-activity sites of srt A. The missense mutation rates of the two groups did not exhibit statistically significant differences. Conclusion There were no genetic polymorphisms of the sortase A gene associated with early childhood caries in two-year-old children.