Effects of antiseptics on Streptococcus gordonii biofilms

Objective: Streptococcus gordonii is a commensal dental plaque microorganism that is 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 antiseptics commonly used in endodontic treatment.

Method: Biofilms of S. gordonii strain DL1 or its isogenic cbdA- or sspA/sspB-deficient derivatives were grown in Todd Hewitt medium in microtiter plates for eight hours. Planktonic cells were aspirated and the remaining 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 re-washed, pulsed for 10 minutes with either 5.25% sodium hypochlorite (NaOCl), 0.12% chlorhexidine digluconate (CHX) or BioPureMTAD^®.  Residual antiseptic was removed with buffer washing, fresh medium was added and biofilm survivor cell growth was monitored spectrophotometrically for 24 hours and confirmed by viable counts.

Result: Unprotected biofilm cells of all three strains were similarly killed by CHX, NaOCl and BioPureMTAD^®.  Of the three antiseptics, CHX was most effective at killing strain DL1 in the presence of all three protectants. Collagen, serum and saliva significantly protected strain DL1 from all three antiseptics compared to buffer-protected cells (p < 0.04).  However, the cbdA and sspA/sspB mutant strains were significantly more susceptible to all antiseptics than strain DL1 (p < 0.001) in the presence of protectants.

Conclusion: The results suggest that S. gordonii surface proteins CbdA, SspA and SspB that may interact with collagen or similar components in serum and saliva may play a role in protecting these bacteria from antiseptics used in endodontic treatment.