Role of the cell membrane in pH-dependent fluoride inhibition of glucose uptake by Streptococcus mutans

Abstract

The effect of pH on the fluoride sensitivity of glucose uptake by whole cells and glucose transport by permeabilized cells of Streptococcus mutans was compared. Whole cells exhibited a marked pH-dependent sensitivity to fluoride over the pH range 7.0 to 5.0. As the pH was decreased, fluoride sensitivity increased. In contrast, no significant effect of pH on the fluoride sensitivity of glucose transport (e.g., phosphorylation) by permeabilized cells energized with 2-phosphoglycerate was noted. The relative effect of pH on the fluoride sensitivity of whole cell glucose uptake and fermentation was similar. These data are consistent with the notion that the cell membrane is impermeable to the fluoride anion and that intracellular accumulation of fluoride depends on translocation of hydrogen fluoride across the membrane.Streptococcus mutans is a colonizer of the human tooth surface and is associated with the development of dental caries in humans (5,6,15). This organism is noted for its aciduric, as well as its acidogenic, properties relative to those of other common plaque microorganisms (8,9,15). Development of dental caries is thought to depend on the acid demineralization of tooth enamel as a direct result of the acidic fermentative activities of S. mutans and other plaque microbes (15). Plaque pH varies from near neutral values in the resting state (no fermentable substrates available) to well below pH 5 during periods of exposure to fermentable substrates (15). Fluoride is a well-known cariostatic agent which is responsible for a major reduction in the prevalence of dental caries (2, 12). The principal cariostatic effect of fluoride is considered to depend on its incorporation into the enamel crystal structure with a resulting decrease in acid susceptibility of the tooth mineral (14). Fluoride also has inhibitory effects on numerous enzymes (17) and on the fermentative activities and viability of oral microbes, including S. mutans (for reviews, see references 7, 11, 13, and 16). The fluoride sensitivity of S. mutans sugar fermentation and growth is generally increased as the pH is decreased (1,7,11,16). It has been suggested that the pH-dependent nature of fluoride sensitivity is based on the passive permeability of the cell membrane to HF and impermeability to fluoride anion (16). As the pH of the environment is decreased, the absolute concentration of HF is increased (pK, -3.45) and the pH difference across the cell membrane promotes accumulation of fluoride into the more alkaline cell cytoplasm. This model is supported by the observation that the intracellular accumulation of fluoride increases with the magnitude of the pH difference across the cell membrane of S. mutans (16). In light of these observations, we chose to investigate the role of the cell membrane in the pH sensitivity of fluoride inhibition of glucose uptake and transport by S. mutans over the pH range commonly encountered in plaque. If the model described above is correct, whole cell glucose uptake, but not glucose transport by permeabilized ...

Diminished Acid Tolerance of Plaque Bacteria Caused by Fluoride

“…This reduction could reduce sugar uptake, which appears at low pH values to depend on pmf-associated systems more than on phosphotransferase systems (Hamilton, 1986). In fact, phosphotransferase systems appear to be rather acid-sensitive (Germaine and Tellefson, 1986).…”

Antibacterial activity of glass–ionomer cements, compomers and resin composites: relationship between acidity and material setting phase

“…Fluoride release from these material combined with a pH fall around the material seems to be the most probable reason of the perturbation of Streptococcus metabolism (6). Fluoride has inhibitory effects on numerous enzymes and on the fermentative activities and viability of S. mutans (28). The pH‐dependent fluoride sensitivity of S. mutans is based on the membrane permeability of HF and the membrane impermeability of fluoride anion over the pH range encountered in dental plaque.…”

“…The pH‐dependent fluoride sensitivity of S. mutans is based on the membrane permeability of HF and the membrane impermeability of fluoride anion over the pH range encountered in dental plaque. An earlier examination of fluoride accumulation by resting cell suspensions of S. mutans at different pHs had showed that the magnitude of accumulation was proportional to the pH gradient across the cell membrane (28). Seppä et al .…”

Biochemistry of the Elemental Halogens and Inorganic Halides

“…Although other mechanistic interpretations have emerged, continuing studies on the effect of F -on microorganisms of dental plaque indicate that it is likely that inhibition of growth of acid-producing bacteria contributes to cariostatic action (Hamilton, 1977;Germaine and Tellefson, 1986b). For example, F -has been shown to inhibit the phosphoenolpyruvatedependent transport of sugars across the cell membrane of such enamelcolonizing bacteria as Streptococcus mutans (Germaine and Tellefson, 1986a). Despite well-documented inhibition of bacterial growth in vitro by F -, its low in vivo oral concentration has led to questions as to whether a similar inhibition could play a role in its cariostatic activity.…”

“…A lower pH also results in more efficient passive uptake of F-(as HF) into the cell. The intracellular pH of the oral bacteria is significantly higher, and F -(as F -) becomes concentrated by this pH gradient (Germaine and Tellefson, 1986a). …”