Some antibacterial properties of chlorhexidine

The use of the antiseptic chlorhexidine as a therapeutic or prophylactic drug in dental or periodontal hygiene is a departure from the usual fields of use for this agent. Therefore, a review of some of its antibacterial properties is desirable. The bacteriostatic spectrum of chlorhexidine * was determined: there was a wide spectrum of activity with gram‐positive cocci being especially sensitive (MIC 0.19 to 2.0 μg/ml). Exposure of suspensions of various bacterial species to chlorhexidine (0.02%) for 10 minutes at room temperature, reduced the viable organisms by about 99.99% in most instances. Addition of serum to the test system reduced the bactericidal action markedly. A study with Streptococcus mutans revealed that the presence of sucrose (5%) in the growth‐medium used for preparing bacterial suspensions, profoundly influenced the bactericidal activity. This is presumed to be the result off adsorption of chlorhexidine to extracellular polysaccharides. Attempts to select Escherichia coli and oral streptococci resistant to chlorhexidine by serial passage in subinhibitory concentrations in vitro , indicated that mutants were rare. In contrast, mutants of E. coli resistant to ampicillin or streptomycin were selected with ease. Predictions of what might happen under clinical conditions (where oral organisms might be exposed to sublethal concentrations for very long periods of time) cannot be made from such laboratory experiments. No changes were observed in the susceptibility of faecal organisms of hamsters given chlorhexidine (50 mg/kg) daily by gastric catheter for 28 days but 100 mg/kg rapidly caused a lethal enteritis which was assumed to be the result of gross disturbances of the alimentary microflora. A small study in three human volunteers is reported. Use of a mouthrinse (twice a day for up to seven weeks) containing chlorhexidine digluconate (0.2%) resulted in a slight but transient change in susceptibility of salivary organisms to the bacteriostatic action of the agent. Whether resistance will prove to be an obstacle to the use of chlorhexidine in prophylaxis, in the mouth can be decided only with more clinical experience.