Physiology of Oral Bacteria:  Sugar, Ph, and F

Germaine, Greg

Abstract

Streptococcus mutans, Streptococcus sanguis, Streptococcus mitis and Actinomyces viscosus are prominent members of the oral microflor in humans and associated with development of dental caries (especially S. mutans). The especially prominent cariogenic potential of S. mutans has been suggested to be a result, in part, of the organism's greater aciduric nature relative to the other organisms listed. In addition, fluoride (F) is a widely-recognized major factor in declining caries prevalence, yet we know little of its basis of action(s) on the oral microflora and of those factors that determines the degree of F sensitivity or resistance of particular microbes. In this investigation, we propose to examine (i) the roles of the pH sensitivity of glucose transport and fermentation in the aciduric properties of the oral microbes listed above and (ii) the roles of pH, rate of glycolysis and sizes of intracellular pools of 2-phosphoglycerate (2PG) and phosphoenolypyruvate (PEP) in the determination of the F sensitivity of glucose transport and metabolism of the test microorganisms. Transport will be studied with 14C-glucose and 3H-2-deoxyglucose (2dG) on whole cell suspensions and permeabilized cells. In whole cells, effects of environmental pH (pHe), intracellular pH (pHi) and the transmembrane proton gradient (DeltapH) will be studied. 14C-benzoate will be used for estimation of pHi and DeltapH. Glycolytic rates, and 2PG and PEP pools will be estimated by a combination of enzymatic methods, 3H-2dG transport and chemical techniques. Finally, the proton permeability of test bacteria will be compared to assess the role of maintenance of pHi to an organism's aciduric nature. It is anticipated that the results of this investigation will aid in our eventual understanding of the mechanisms of S. mutans cariogenesis and the plaque-related cariostatic action of F.