Competition for dietary carbohydrates between streptococci in dental plaque

Abstract

The predominant microorganisms in dental plaque, i.e., streptococci and actinomycetes, are carbohydrate fermenters. In the natural environment these organisms experience carbohydrate limitation interrupted by periods of substrate excess following food intake by the host. Recently, we have studied the competition between pairs of oral Streptococcus species in the chemostat under continuous glucose or sucrose limitation and under glucose pulsed conditions. In the present study we have investigated the competition for dietary carbohydrates in dental plaque of gnotobiotic rats infected with the same combinations of streptococci. The rats were exposed to similar regimes of carbohydrate administration as in the chemostat by incorporation of low molecular carbohydrates in the diet and drinking water. Addition of glucose to the diet favoured the organism with the highest qmax for glucose. This result parallels the outcome of earlier competition experiments in glucose-pulsed chemostats, which showed that the organism with the highest qmax glucose became dominant in the cultures. Previous observations that bacteriocin production and extracellular glucan synthesis are major ecological factors for oral streptococci were also confirmed in this experiment.