Morphology Changes and Inhibition of Enzymes Production During PAE Induced by Clindamycin and Chlorhexidine Against Oral Streptococci

The study was conducted to determine the post antibiotic effect (PAE) of clindamycin and/or chlorhexidine against clinical isolates of oral streptococci. The PAE period was determined by spectrophotometric technique. A prolonged period of PAE (4h) was demonstrated when the isolate of Streptococcus mutans was exposed for an hour at a concentration of 4XMIC of clindamycin. While exposure to clindamycin at sub-MIC (1/4 and 1/8 XMIC) induced a short period (0.8 & 1h) under the same conditions. However, a short period (0.2 h) was obtained when the other isolate of Streptococcus mutans exposed to chlorhexidine at supra-MIC (8XMIC) for an hour under the same conditions. The impact of PAE on cell morphology and physiology during PAE was demonstrated. Thus, the morphology of streptococci was changed during PAE induced by 1⁄2 and 2XMIC of clindamycin. A marked reduction in cell surface hydrophobicity was observed upon exposure of the cells to clindamycin and chlorhexidine at 2XMIC for an hour. A significant decrease in elastase production by Streptococcus mutans was observed during PAE when the cells were exposed to 4XMIC of chlorhexidine. The hemolysin activity was significantly reduced by 30% during PAE induced by exposure of the cells to 2XMIC of both clindamycin and chlorhexidine for an hour.