Effect of extracellular polysaccharides on diffusion of NaF and [14C]-sucrose in human dental plaque and in sediments of the bacterium Streptococcus sanguis 804 (NCTC 10904).

It has been postulated that extracellular polysaccharides form a barrier to diffusion in dental plaque. Diffusion coefficients, D, were measured for NaF and [14C]-sucrose in glucan-free and glucan-containing sediments of Strep. sanguis 804 at 37 degrees C. There was a tendency for NaF and [14C]-sucrose to diffuse faster as the carbohydrate concentration in the sediments increased. NaF diffused only 38 per cent more slowly in cell-free glucan sediment than in water, suggesting that glucan per se does not form a barrier to diffusion. The diffusion coefficient for NaF was positively correlated with carbohydrate concentration in individual plaque samples from 15 subjects and incubation of 3 plaque samples with sucrose resulted in both an increase in carbohydrate concentration in the plaque and an increase in D for NaF. Thus the presence of extracellular polysaccharides in plaque leads to slightly faster rates of diffusion. Nevertheless, the total time for diffusion through plaque may be increased if the presence of extracellular polysaccharides results in thicker layers of plaque.