INFECTIVITY OF A GLUCAN SYNTHESIS-DEFECTIVE MUTANT OF STREPTOCOCCUS-GORDONII (CHALLIS) IN A RAT ENDOCARDITIS MODEL

Streptococcus gordonii, a member of the human indigenous oral microflo ra, colonizes smooth tooth surfaces and contributes to dental plaque f ormation. Although it is not recognized as being a cariogenic pathogen , it may cause endocarditis following invasion of the bloodstream. Usi ng allelic exchange mutagenesis, we have constructed a mutant of S. go rdonii (Challis) which is defective in its single functional glucosylt ransferase gene and, hence, is unable to synthesize glucan exopolymers from sucrose. When examined in a rat endocarditis model, the sucrose- grown mutant did not differ significantly from S. gordonii wild-type, suggesting that glucan polymers did not contribute to infectivity. Thi s result was in striking contrast to that previously observed with a p olymer-defective S. mutans mutant.