Journal of Dental Research, Vol 65, 895-898, Copyright © 1986 by International & American Associations for Dental Research Online Journals
The effects of sorbate on oral streptococci grown in continuous culture
A. H. Rogers
The antimicrobial effect of potassium sorbate on Streptococcus mutans and
S. milleri grown in continuous culture was determined at pH values of 7.0,
5.5, and 5.0. Organisms were grown glucose-limited at a dilution rate of D
= 0.1 h-1, corresponding to a doubling time of ca. seven hours, in a
chemically defined medium under an atmosphere of 5% CO2 in N2. After
equilibration at the appropriate pH level, the culture vessel was pulsed
with potassium sorbate to a final concentration of 20 mmol L-1 or with
sorbate followed almost immediately by a pulse of glucose (to 40 mmol L-1);
that is, the cultures were exposed to transient excesses of sorbate with
and without glucose--such as might occur during meals. At pH 7.0, sorbate
had virtually no effect on glucose uptake and on the, albeit transient,
increase in growth rate and acid production by both organisms. At pH 5.5
and 5.0, both cell viability and acid production in S. milleri were
depressed following a pulse of sorbate, the effect being even more marked
after a sorbate/glucose pulse. At low pH, the uptake of glucose in the
presence of sorbate was drastically reduced. The effect on S. mutans was
less marked, but growth and acid production were greatly depressed at pH
5.0 following consecutive pulses of sorbate. The antimicrobial effect of
the widely used preservative potassium sorbate, at low pH, is confirmed for
oral streptococci, and it is suggested that continuous culture offers a
relevant system for testing potential antimicrobial agents.
