The effect of sab-inhibitory concentrations of chlorhexidine on the proteolytic activity of Bacteroides gingivalis

Abstract

Bacteroides gingivalis was grown in the presence of chlorhexidine at concentrations lower than the minimum inhibitory concentration (1·25 mg/l). These sub-inhibitory concentrations were found to stimulate growth in terms of an increase in the number of viable cells, the greatest increase being at a concentration of 0·75 mg/l of chlorhexidine. The total proteolytic activity of the cultures (assayed by means of azocasein hydrolysis) grown in the presence of chlorhexidine and their specific activities (per 10⁶ cells) were found to be less than those of the cultures grown in the absence of chlorhexidine. In the case of the trypsin-like activity of the micro-organism, a different pattern was found. Thus, although the specific activities of the chlorhexidine-grown cultures were lower than those of the chlorhexidine-free cultures, the total activity in the chlorhexidine-grown cultures was greater.