Examination of caries-risk person by selective media for S.mutans and S.sobrinus

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The aim of this study was to improve the selective medium of Streptococcus mutans. A new selective medium, designated MS-MUTV, was prepared by adding 10mg/l valinomycin to the MS-MUT medium previously described.The average recovery of S.mutans was 72.1% and growth of S.sobrinus, S.anginousus group was inhibited on MS-MUTV, but allowed on MS-MUT. One hundred and thirty-nine human saliva samples were examined and counted for S.mutans and non-S.mutans colonies. The recovery of S.mutans on MS-MUTV was similar to that on MS-MUT. Eighty-two and 7.9 percent of the saliva samples obtained S.mutans pure cultures with no bacterial growth on MS-MUTV, respectively. The remaining 10.1% were contaminated with non-S.mutans with low level CFU. MS-MUTV is useful for isolation of S.mutans alone from clinical samples in routine examinations.The aim of this study was to clarify the correlation between caries prevalence and qualitative difference of S.mutans. Ten caries-susceptible and ten caries-free persons were selected in dental school. Their saliva was collected, and one IS.mutans strain was isolated from each subject and then identified. The insoluble glucan synthesis, sucrose-dependent firm colonization, the acid productivity, the acid tolerance and the expression of gtfB in S.mutans isolates from both groups were compared. As to the firm colonization ability, the final pH test of acid productivity, the acid tolerance and the expression of gtfB, there were no significant differences between S.mutans isolates from both groups.