Effect of human saliva on the fluoride sensitivity of glucose uptake by Streptococcus mutans

Abstract

The fluoride (F) sensitivity of glucose uptake by whole cell suspensions of Streptococcus mutans in the presence and absence of human whole salivary supernatant was studied. It was observed that dithiothreitol (DTT) and other thiols markedly reduced the F sensitivity of cells when saliva (50%, vol/vol) was present during glucose uptake. In the absence of saliva, cells were sensitive to 2 to 2.5 mM F regardless of the presence of thiols. Supplementation of cells in phosphate or tris(hydroxymethyl)aminomethane-hydrochloride buffers with physiological concentrations of calcium or phosphate had no effect on the F sensitivity of the organism. Experiments with permeabilized cells suggested that thiols themselves had no direct effect on the F sensitivity of enolase (a principal F target). Cells pretreated with DTT subsequently exhibited decreased F sensitivity when examined in the presence of saliva but not in the absence of saliva. Cells pretreated with whole salivary supernatant were found to be subsequently less sensitive to F in the absence of saliva during glucose uptake. Furthermore, in cases where cells were pretreated with saliva, subsequent additions of DTT were unnecessary to obtain maximal reduction in the F sensitivity of glucose uptake. It was concluded that the saliva-dependent reduction in F sensitivity of glucose uptake was not due to sequesteration of available F by salivary constituents. The data suggest that a salivary component(s) interacts directly with the microorganism in some manner which results in reduced F sensitivity of the process under study. Possible mechanisms of saliva action are discussed. 'Dialyzed for 18 h at 4°C against 200 volumes of distilled water. INFECT. IMMUN.

Effect of endogenous phosphoenolpyruvate potential on fluoride inhibition of glucose uptake by Streptococcus mutans

“…Note that a family of uptake profiles was obtained in which fluoride inhibition was reduced as the glucose concentration used in pretreatment was increased. The marked curvilinear form of glucose uptake apparent with glucose pretreatments of less than 50 pM are similar to those observed with saliva-pretreated cells (7).…”

“…that 2PG effectively reduced the inhibitory effect of fluoride )lase by fluoride, one should be able to reduce on PEP synthesis as judged by 2-dG transport. We reported iibition of transport in permeabilized cells ener-previously that S. mutans incubated in saliva exhibited 2PG by simply increasing the concentrations of fluoride-resistant glucose uptake (6,7). We also reported Furthermore, permeabilized cells energized with that whole saliva supernatant and parotid fluid promoted J be refractory to fluoride inhibition.…”

“…We reported earlier that saliva had a pronounced effect on the fluoride sensitivity of glucose uptake by Streptococcus mutans (7). Cells suspended in saliva exhibited a fluorideresistant uptake component that was absent in cells suspended in buffer.…”

“…Thus, the relative effects of 100 to 200 ,uM glucose and 80% saliva on establishment of a PEP potential are similar. It is also of interest to note the similarity in fluoride sensitivity of S. mutans pretreated with saliva (7) or glucose (Fig. 1).…”

“…Therefore, any condition that increased intracellular 2PG might also be associated with a reduced sensitivity of sugar transport to fluoride inhibition. Thus, the reduced fluoride sensitivity of glucose uptake by S. mutans in the presence of saliva reported earlier (7) might have been due to the establishment of a PEP potential at the expense of salivary constituents such as glycoprotein-associated carbohydrate (10). We report here that accumulation of a PEP potential by S. mutans will, indeed, result in reduced fluoride sensitivity of glucose uptake.…”