The Differential Effects of Antimicrobials on Streptococcus gordonii Biofilms
Violante, Timothy Luke
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Objective: Streptococcus gordonii is a commensal dental plaque microorganism that is also found in primary and persistent endodontic infections. Studies have suggested that bacterial surface proteins may interact with host components to protect bacteria from antimicrobial agents. The objective of this study was to test the hypothesis that S. gordonii collagen-binding proteins CbdA, SspA and SspB may play a role in protecting S. gordonii from oral antiseptics. Methods : Eight-hour biofilms of S. gordonii strain DL1 and its isogenic cbd A- and ssp A/ ssp B-deficient derivatives were grown in Todd Hewitt (TH) medium in microtiter plates. After aspiration of planktonic cells, biofilm cells were washed with buffer, then incubated for 30 minutes with either pH-adjusted buffer or putative protectants: whole saliva, heat-treated serum, or type I collagen. Biofilms were washed again, pulsed for 10 minutes with either 5.25% sodium hypochlorite (NaOCl), aqueous saturated calcium hydroxide (Ca(OH) 2 ), 0.12% chlorhexidine digluconate (CHX), BioPure® MTAD®, 0.3% Triclosan or full strength Listerine® (Cool Mint or Zero). Biofilms were washed to remove residual antiseptic, fresh TH was added and survivor cell growth was monitored spectrophotometrically for 24 hours. Results: In the absence of collagen, serum, and saliva biofilm cells of all strains were killed by CHX, NaOCl and Listerine® Zero, whereas some cells survived Ca(OH) 2 and Listerine® Cool Mint pulses. In the presence of collagen, serum, and saliva, parental and mutant cells were differentially protected from all antiseptics except CHX; protectants provided minimal protection to parental DL1 cells, but no protection to mutants. Notably, strains lacking CbdA, SspA and SspB were less protected by collagen and serum from NaOCl, Ca(OH) 2 , and Listerine® formulations than the parental strain. Conclusion: Taken together, these results suggest that S. gordonii collagen-binding-protein-deficient mutants were more susceptible than parental cells to NaOCl, Ca(OH) 2 , Listerine® Cool Mint and Listerine® Zero when collagen and serum were present. These findings may have implications for clinical efficacy of these antiseptics.