Fluoride Uptake and Fluoride Resistance in Oral Streptococci

Abstract

Fluoride uptake was examined in the highly F-sensitive Streptococcus salivarius strain 25975, the F-resistant mutant Flr103, and the relatively insensitive S. sanguis H7PR3. F was taken up by all strains from media at neutral pH, containing 1 or 10 micrograms F/ml (0.053-0.526 mmol/L), and uptake was directly proportional to the delta pH that was maintained by the cells. The final intracellular concentrations of F in the F-resistant strains were higher than those in the F-sensitive strain. Similar differences in F uptake were observed in buffer at pH 5.5, although both delta pH and F uptake were higher in all strains at the lower pH. These experiments demonstrate that resistance to F does not necessarily involve the exclusion of F from the cells. The lower uptake of F by F-sensitive cells is attributed to the finding that F dissipates the transmembrane pH gradient, and this, in turn, limits the concentration of intracellular F.

The Effect of Fluorhydroxyapatite-derived Fluoride on Acid Production by Streptococci

“…In the present study, where the percentage of mineral dissolved was as low as 2%, this non-stoichiometric dissolution would be expected to be even more pronounced and would account largely for the low fluoride values. Fluoride is known to be taken up from solution by bacteria (Kashket and Preman, 1985), but calculations show that this could account for only a small part of the discrepancy between predicted and observed values of fluoride in our reactions. It is suggested, therefore, that if the metabolic events described in this study could have been cycled repeatedly to dissolve a greater proportion of the mineral reservoir, then much higher fluoride concentrations in the order of 0.35 mmol/L (6.7 ppm) may have been obtained (Pearce et al, 1995), and a more marked effect of fluoride seen.…”

In vitro Demineralization of Enamel by F-sensitive and F-resistant Mutans Streptococci in the Presence of 0, 0.05, or 0.5 mmol/L NaF

“…Accumulation of fluoride will occur when intracellular pH is more alkaline than extracellular pH (Eisenberg and Marquis, 1980;Kashket and Preman, 1985). At lower environmental pH, cells may be more effectively inhibited by fluoride because of a greater uptake of it as a result of greater amounts of protonated fluoride and increased pH gradients across the cell membranes.…”

Biochemical Effects of Fluoride on Oral Bacteria

“…This important relationship between .6.pH and F uptake has been confirmed and extended in more recent studies Vicaretti et al, 1984;Kashket and Preman, Some Enzymes Acid phosphatase Pyrophosphatase Pyrophosphorylase Peroxidase Catalase 1985) and is the basis of the well-established 'F/pH effect' described originally by Borei (1945). Of interest in these studies was the observation that fluoride was taken up into cells at pH 7, although concentrative uptake was only observed at acidic pH values (Vicaretti et al, 1984;Kashket and Preman, 1985). Fluoride-resistant organisms, such as Lactobacillus casei, appear to avoid the inhibiting effects of F by maintaining a negligible .6.pH until the external pH is near 5.0, while fluoridesensitive organisms, such as S. mutans, generate increasingly larger pH gradients as the pH is decreased from 7.0 .…”

“…Small, but perceptible, inhibition can be observed at extracellular F levels as low as 53 urnol/L (Bibby and van Kesteren, 1940;Kashket et aI., 1977) when the intracellular F concentration can be near 320 urnol/L (Kashket and Preman, 1985). There is perhaps a misconception that these small anti-microbial effects of fluoride are of no consequence in the 'real world' of dental plaque.…”