Induction Of Fluoride-resistant Strains Of Streptococcus Sobrinus 6715 And Study Of Its Acidogenesis In Vitro

Objective: To induce fluoride-resistant strain of S. sobrinus6715 in vitro and find out its differences of cariogenicity to the parent strain. Methods: Fluoride-resistant strain S. sobrinus 6715-FR was obtained by subculturing S. sobrinus 6715 to TSA containing different concentrations of fluoride in mini-oxygenium gradually, then were subcultured to PYG with its parent strain simultaneously by anaerobic cultivation, Lactic production of media were measured by HPLC method and terminal pH recorded by pH meter. Results: The stable fluoride-resistant strain of S. sobrinus6715 was induced successfully in vitro;Lactic production of 6715-FR was significantly more than its parent strain at various initial pH values with 5.0 mmol/L fluoride, whereas when no fluoride existed, its acid production was more than S. sobrinus 6715 at initial pH above 5.5 while the result was opposite when pH was 5.5 below (p<0.05) . lactic production of 6715-FR tended to be more than its parent strain at various initial pH values with 0.5mmol/L fluoride, though not significant statistically(p > 0.05).Concltsion: Compare to parent strain of S. sobrinus 6715,the fluoride-resistant strain 6715-FR has higher acidogenesis than its parent strain in fluoride existence, expacilly in high fluoride concentration. Which indicates that the fluoride-resistant strain 6715-FR has a cariogenic potential regardless of fluoride existence or not, and has stronger cariogenic potential than its parent strain in fluoride existence.