INHIBITION BY ETHANOL OF THE GROWTH OF BIOFILM AND DISPERSED MICROCOSM DENTAL PLAQUES

Inhibition of microcosm plaque biofilm growth by periodic application of ethanol was compared with the minimum inhibitory concentration (MIC ) and bactericidal effects of ethanol on liquid cultures of dispersed plaque bacteria. Microcosm plaques were cultured from saliva in a mult iplaque 'artificial mouth' and their growth in wet weight measured dai ly. Nutrient conditions included: a continuous supply of a medium cont aining 0.25% mucin, and 8-hourly 5% (w/v) sucrose (1.5 ml over 6 min). Plaque biofilm growth was strongly inhibited by exposure to 40% (v/v) ethanol applied in volumes of 3.75 ml over 15 min, six times daily. A pplication df 1.5 ml over 6 min inhibited much less or not at all. Eth anol concentrations lower than 40% caused less inhibition, with 10% ha ving almost no effect. The pH response to sucrose was unchanged by pri or application of 40% ethanol for 30 min. Some evidence was obtained f or either bacterial adaptation to ethanol or selection of ethanol-resi stant bacteria. The MIC and bactericidal effects of ethanol were asses sed by growth of dispersed plaque in liquid culture; the bactericidal effect was measured as the induced delay in growth. The aerobic and an aerobic MIC of ethanol for growth was 10% and 8%; 50% inhibition of gr owth rate occurred at 3.7% and 2.8%. Ethanol (40%) was bactericidal wi thin 1-2 min, but 10% had almost no effect. It was concluded that, des pite the well-known high ethanol sensitivity of dispersed plaque bacte ria, prolonged application of ethanol concentrations in the order of 4 0% are necessary to inhibit growth of plaque biofilms.