Synergistic, Growth-inhibitory Effects of Chlorhexidine and Copper Combinations on Streptococcus mutans, Actinomyces viscosus, and Actinomyces naeslundil

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Abstract
The purpose of this investigation was to determine whether chlorhexidine combined with copper would exert a synergistic, growth-inhibitory effect against selected oral bacteria. Actinomyces viscosus, Actinomyces naeslundii, and Streptococcus mutans were all susceptible to chlorhexidine individually, with S. mutans displaying the highest sensitivity. Much higher concentrations of copper were needed to achieve growth inhibition of the micro-organisms tested. Determination of minimum inhibitory concentrations (MICs) of chlorhexidine and Cu2+ combinations suggested synergistic activity. Bactericidal kinetics assays confirmed synergism of chlorhexidine and Cu2+ combinations with 1 to 2 log greater decreases in viable cell numbers compared with chlorhexidine alone. Under the constraints of the conditions employed, these data demonstrate the efficacy of chlorhexidine and Cu2+ combinations against the oral bacteria tested. These studies suggest that a chlorhexidine and copper formulation could be useful as a mouthrinse in helping control cariogenic micro-organisms and/or in the treatment of gingivitis.