The effect of surface adsorption and staining reactions on the antimicrobial properties of some cationic antiseptic mouthwashes.

The phenomenon of surface adsorption appears fundamental to the antiplaque activity of the cationic antiseptics. Moreover, reaction with chromogenic material is relevant to the local side effect of staining. The purpose of this investigation was to determine how such local reactions affect the antibacterial activity of some of these antiseptics. The minimum inhibitory concentration (MIC) of commercial mouthrinses containing alexidine, cetyl pyridinium chloride, chlorhexidine gluconate and hexetidine against Oxford staphylococcus (NCTC 6571) and Escherichia coli (NCTC 10418) was established by tube dilution. The effect on the MIC values against O. staphylococcus of adding polymethylmethacrylate polymer or against E coli of adding a standard tea solution was then measured. The zones of inhibition around acrylic blocks soaked in the respective antiseptics, with and without postexposure washings, were measured. The effects on zone width of placing the antiseptic-soaked blocks in tea were recorded. The MIC values of alexidine, cetyl pyridinium chloride and chlorhexidine gluconate, but not hexetidine, were all increased by adding polymethylmethacrylate to cultures. Tea added to the culture increased the MIC values against E. coli for alexidine, chlorhexidine and hexetidine, but not for cetyl pyridinium chloride. Zones of inhibition around antiseptic-treated blocks were reduced by washing and, in the case of hexetidine, completely abolished. Tea-soaking further reduced the zones of inhibition for alexidine and chlorhexidine, but not cetyl pyridinium chloride.(ABSTRACT TRUNCATED AT 250 WORDS)