Post-antibiotic effects and post-antibiotic sub-minimal inhibitory concentration effects of chlorhexidine against oral bacteria

Abstract

Post-antibiotic effect (PAE) is defined as the suppression of bacterial growth for a particular duration after brief exposure to an antimicrobial agent. Chlorhexidine is a widely used biocide found in antiseptic products; however, its PAE remains unclear. In this study, PAE, post-antibiotic sub-minimum inhibitory concentration (MIC) effects (PA-SME), and sub-MIC effects (SME) of chlorhexidine on oral bacteria were investigated. For PAE measurement, bacteria were exposed to 10× MIC chlorhexidine for 1 min, which was then eliminated by washing. For determining PA-SME, bacteria were exposed to 0.1, 0.2, and 0.3× MIC chlorhexidine during the post-antibiotic phase and to sub-MIC chlorhexidine for the measurement of SME. PAE, PA-SME, and SME of chlorhexidine were observed. The PAE lasted for 0.9 hr for Streptococcus mutans , 0.1 hr for Streptococcus gordonii , and 0.35 hr for Lactobacillus acidophilus. The PA-SME against oral bacteria lasted for a longer duration with increasing chlorhexidine concentrations. The PA-SME against oral bacteria lasted for a substantially longer period than SME did. The present study illustrates the existence of chlorhexidineinduced PAE, PA-SME, and SME against oral bacteria, thereby extending the pharmacodynamic advantages of chlorhexidine.