Methods: An ATCC 12104, Ao WVU 627, Sm NCTC 10449 and Ss ATCC10566 were used. The bacteria were grown in a complex medium containing 0.5% glucose, 0.1% ammonium bicarbonate and potassium fluoride (0-225 ppm F) anaerobically. The growth rate was estimated as doubling time calculated from growth curve obtained by optical density at 660 nm. In addition, the fluoride effect on growth was compared with that on acid production, which had been reported by the authors previously.
Results: In the presence of 90-ppm F, the doubling time (regarded as 100 in the absence of fluoride) of An and Ao increased to 144±44 and 162±8, respectively. Meanwhile, that of Sm and Ss increased to 844±462 and 690±459, respectively. The tendency of fluoride inhibition on growth was similar to that on acid production, although the growth of An was more sensitive to fluoride than its acid production.
Conclusions: This study indicated that, in terms of growth as well as acid production, Actinomyces was more tolerant to fluoride than Streptococcus. In addition, the growth of An was more sensitive to fluoride than its acid production, suggesting that fluoride can inhibit not only acid production responsible for energy production, but also other biochemical processes involved in growth, such as protein syntheses.