Phenotypes of Streptococcus mutans isolates in sound and cavitated tooth surfaces and its relationship to early childhood caries in China

Background To compare the phenotypes of Streptococcus mutans (S. mutans ) strains isolated from sites with different caries susceptibility of a single subject. Methods This study was carried out in children with early-childhood caries (ECC) and caries-free (CF). The ECC subjects presented two sites: a cavitated lesion (ECC-C) and a sound surface (ECC-F). The CF subjects presented one sound surface. The following phenotypes were evaluated among these three sites: growth pattern, biofilm, exopolysaccharide (EPS), pH drop, and the expression levels of genes (gtfB, gtfC, spaP, srtA, relA, ffh, srn225147, and srn821798). Results All of these phenotypes were detected similarly between ECC-C and ECC-F groups. However, the capacity of biofilm formation, EPS, pH drop and the expression levels of genes (gtfB and spaP) of S. mutans in the CF group were lower compared to those of the ECC group. There was a relatively higher expression of srn821798 compared to that of srn225147 in clinical isolates, and isolates with low expression of srn821798 had lower expression levels of predicted targets (gtfB, gtfC, and spaP). Conclusions These data indicate S. mutans isolated from sites with different caries susceptibility of a single subject showed similar characteristics, while the cariogenic potential of the S. mutans isolated from ECC individuals was relatively higher than that of CF subjects.