Biofilm formation and demineralization by mutans streptococci from human and chimpanzee

Objectives: New strain of mutans streptococci (MS), Streptococcus troglodytae, was isolated from chimpanzee oral cavity. Another MS, Streptococcus dentirousetti, was also isolated from chimpanzee. These MS were reported to form biofilm in the presence of sucrose and to possess glucosyltransferases like Streptococcus mutans. The purpose of this study was to compare abilities of S. troglodytae and S. dentirousetti with S. mutans to form biofilm on enamel surface and to demineralize the enamel by using artificial mouth model system (AMS).
Methods: S. mutans ATCC 25175, S. troglodytae TKU31 and S. dentirousetti TKU32 were used. In the AMS, four enamel slabs (3.5x3.5x1.5mm) were set on the Teflon adaptor around flat bulb of pH electrode. This electrode was set upside down in the vessel of AMS. Each bacterial suspension (OD540=1.0), Tryptic Soy broth without dextrose supplied with 2.5% sucrose and PBS were dropped on the electrode by peristaltic pump. The pH values underneath biofilm formed on the flat electrode were recorded continuously. The amount of biofilm was assessed by measuring turbidity of bacterial cells at 540nm. Enamel demineralization was measured by Vicker's microhardness tester.
Results: The pH values underneath the biofilm on the electrode in S. mutans and S. dentirousetti began to decrease after 4h operation of AMS and reached 4.1 and 4.4 after 16h, respectively. The pH value in S. troglodytae, decreased slowly and reached 4.6 after 24h. The amounts of biofilm were 0.100+/-0.028, 0.147+/-0.035, 0.280+/-0.095 in S. mutans, S. troglodytae and S. dentirousetti, respectively. The difference of microhardness of enamel (delta H) before and after AMS operation were 175.9+/-28.6, 105.7+/-29.9, 281.7+/-17.3 in S. mutans, S. troglodytae and S. dentirousetti, respectively. Glucosyltransferase and acid fermentation of these strains should be ascribed to biofilm formation and subsequent enamel demineralization.
Conclusions: S. troglodytae and S. dentirousetti from chimpanzee showed cariogenic property like S. mutans.