Cariogenic virulence of Streptococcus mutans AHT mutants with altered in vitro adherence abilities in hamsters

Plaque-forming ability and cariogenic virulence of Streptococcus mutans AHT mutants having varying in vitro adherence abilities were studied in hamsters reared on a high sucrose diet over a period of 64 days. The parent wild-type strain produced heavy plaque and extensive carious lesions on molars. However, mutants M1, M2, and M13, which have lost the ability to form adhesive deposits on glass when grown in sucrose broth, and mutant M9, which adheres firmly to glass but in an extremely small amount, could not be recovered from the mouths of animals even after repeated inoculations at weekly intervals throughout the experimental period. Mutant M35, which produces a large amount of loosely adhering deposits in vitro, became established and persisted on molars, but its recovery was extremely low. None of the mutants, including M35, significantly produced plaque and caries in hamsters. Possible causes of this inability to form plaque and the avirulence of mutants are discussed.