Abstract
An attempt has been made to monitor colonization of S. mutans in fissures of rat molars, and bacterial flora of both fissures and oral cavity have been examined during the progress of tooth eruption.
During this examination S. mutans strains which exhibited unique colony morphology on MS and TYC agar were isolated from fissures of rat molars, and their properties were investigated. S. mutans FA-1 and strains freshly isolated from oral cavity were used as control strains.
Molars extracted from rats were dipped into melted wax to sterilize their surfaces and ground into powder. The powder was sonicated in peptone water, and the resulting suspension wasplated on MS and TYC agar, and then incubated anaerobically for 48 hr at 37°C. The isolated strain and control strains were cultured in both modified Minimal and Complete media of Lederberg (1950). The bacterial growth was determined by the turbidity at OD630. Acid production was monitored by pH changes and GLC. The glucosyltransferase (GTase) activity was determined as described by Wenham et al. (1979).
Isolated strains did not synthesize dextran and formed pinpoint colonies on agar plates. Theyformed much longer filamentous chains with cells which were more elongated than control strains.
However, repeated culturing and subsequent plating of the isolated strain on Complete medium revealed increasing numbers of colonies which resembled those of control strains. No difference in lactic acid production and GTase activity was observed between the isolated strain and FA-1, but the freshly isolated strain grew in Minimal medium more rapidly than FA-1 which was inoculated from TYC medium of our stock culture. Repeated culturing of FA-1 in Minimal medium changed its morphology to that of the freshly isolated strain.
This study suggests that the freshly isolated strain may be a mutant of S. mutans, and that the phenotype of S. mutans under the strictly limited conditions in deep fissures may be different from that of S. mutans in the oral cavity.
