Assessment of susceptibility of plaque bacteria to chlorhexidine after six months' oral use

Abstract

Changes in the susceptibility of plaque bacteria to chlorhexidine treatment were investigated by determining the minimum inhibitory concentration (MIC) of chlorhexidine on two kinds of bacteria commonly found in supragingival plaque. Streptococci and actinomyces were isolated from plaque samples collected from subjects participating in a clinical trial comparing a 0.12% chlorhexidine gluconate mouthrinse to a placebo mouthrinse. The isolates were inoculated onto media containing varying concentrations of chlorhexidine to determine the MIC of chlorhexidine during the six‐month treatment period and three months after cessation of treatment. While significant differences in the sensitivity of these two bacterial strains to chlorhexidine were seen sporadically, no consistent pattern of resistance emerged. It was concluded that prolonged use of a 0.12% chlorhexidine gluconate mouthrinse did not alter the composition of the oral microflora toward organisms less sensitive to chlorhexidine. This conclusion was further supported by the clinical findings in this trial that showed chlorhexidine's effects on plaque and gingivitis indices were maintained throughout the six‐month treatment period. Three months after the mouthrinse was discontinued, the MIC's of chlorhexidine on isolates from placebo‐treated and chlorhexidine‐treated subjects were the same as pretreatment values. Thus, no residual change in resistance was observed nor were there any adverse changes in the microbial profile.