Effects of low-concentrated chlorhexidine on growth of Streptococcus sobrinus and primary human gingival fibroblasts
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The aim of this study was to investigate the in vitro effects of low concentrations of chlorhexidine (CHX) on the proliferation of Streptococcus sobrinus (ATCC 33478) and primary human gingival fibroblasts (HGF). Liquid cultures of bacteria or human gingival fibroblasts were exposed to CHX concentrations ranging from 0.07 to 40 μM in microtiter plates at 37°C for 24 h. Bacteria or cells grown without CHX served as controls. The effects of CHX were determined either by measurements of the optical density (OD) of bacterial cultures or by evaluation of cell growth with the DNA-intercalating fluorescent stain H33342 in comparison to untreated controls. Results were evaluated calculating means and standard deviations. Data were statistically analyzed by an ANOVA using Post Hoc tests (p<0.005). No growth inhibition of S. sobrinus was found at concentrations between 0.07 and 0.15 μM CHX, whereas 0.3 μM CHX led to an elongated (2 h more) lag phase and 0.6 μM CHX induced a lag phase of 4 h more and a minor inclination of the curve in the log phase. Concentrations of CHX≥1.25 μM completely inhibited growth of S. sobrinus. On the contrary, CHX showed no significant effect on growth of HGF at concentrations ≤5 μM. A slight growth inhibition was only observed at a concentration of 5 μM. CHX-concentrations of 10 and 20 μM reduced cell growth to 88 or 75% of control assays. Data analysis showed that overall treatment effects were highly significant (p<0.005). Our data reveal that chlorhexidine inhibits proliferation of S. sobrinus even at very low concentrations while concentrations of CHX≤5 μM are not cytotoxic to human gingival fibroblasts.
KeywordsChlorhexidine Streptococcus sobrinus Human gingival fibroblasts Cytotoxicity
The authors would like to thank Mr. Oliver Staperfeld and Mr. Dennis DiJulio for their excellent technical assistance.
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