A Streptococcus gordonii gene similar to ace was identified by genome sequence searches in silico. An isogenic derivative of strain DL1 with a disruption in the identified gene was constructed by allelic replacement. Parent and mutant strains were characterized for their ability to bind immobilized collagen type 1 in a microtiter plate-binding assay. Survival of the strains in a human tooth ex vivo–instrumented root canal model was compared by inoculating canals with parental or mutant bacteria and determining the colony-forming units (CFUs) recovered at various time points over a 12-day period.
The S. gordonii gene, encoding a protein with a conserved collagen-binding domain similar to that of Ace, was designated cbdA. The cbdA-deficient cells were less able to bind collagen type 1 than parental cells (P < .0001). Genetic complementation of the cbdA-deficient strain restored the collagen-binding phenotype. By day 12, significantly fewer (P = .03) cbdA-deficient than parental CFUs were recovered from instrumented canals.
A gene encoding a putative collagen-binding protein was identified in S. gordonii. Fewer S. gordonii cbdA–deficient cells survived ex vivo compared with parental cells, suggesting that collagen-binding proteins may contribute to the persistence of oral streptococci in instrumented root canals.