Journal of Dental Research, Vol 64, 85-89, Copyright © 1985 by International & American Associations for Dental Research Online Journals
Effect of environmental conditions on the fluoride sensitivity of acid production by S. sanguis NCTC 7865
P. D. Marsh, A. S. McDermid, C. W. Keevil and D. C. Ellwood
Growth and environmental conditions affected the fluoride (F) sensitivity
of acid production by Streptococcus sanguis NCTC 7865. Cells grown
glucose-limited in a chemostat were generally more sensitive than those
harvested from cultures in which there was an excess of glucose (amino
acid-limited). There was no consistent relationship between the growth rate
of cells and their F sensitivity. Slower-growing cells (mean generation
time = 14 hr) were more sensitive than those growing quickly when glucose
was the limiting nutrient, whereas the faster growing cells from the
glucose-excess culture were most susceptible. The pH of the environment
markedly affected the F sensitivity of cells: 2 mM F- was sufficient to
abolish acid production by cells incubated at pH 5.0, whereas 24 mM F- did
not totally inhibit glycolysis at pH 7.0 or 8.0. Regardless of pH and
growth conditions, the cationic composition of the environment had the most
pronounced effect on acid production and fluoride sensitivity. Cells washed
and re-suspended in KCl were more acidogenic and more sensitive to F than
the same cells treated with saline. At pH 7.0 and 8.0, saline-washed cells
were comparatively unaffected by F, while glycolysis by the same cells at
the same pH but washed in KCl could be inhibited by up to 80%. These
results suggested that F inhibition could not be explained merely on the
basis of HF uptake at low pH values. Since it has been shown previously
that the activity of the energized membrane is maintained by K+ and
dissipated in the presence of Na+, it was proposed that proton motive force
(pmf) might be involved in the uptake of F-.
