Binding of fluoride by oral bacteria.

Abstract

Interpretation of the proposed actions of fluoride on oral bacteria demands some knowledge of the species as well as the strains of organisms that bind fluoride, the quantity of fluoride attached to these bacteria and the conditions under which such binding occurs. A sensitive Ge(Li) γ-ray spectrometer was used to measure the levels of ^l8F bound by oral bacteria and to check the radiochemical purity of ¹⁸F. Resting cells of <i>Streptococccus mutans</i> LM7 and <i>Staphyiococcus aureus</i> were the most active organisms with regard to ¹⁸F binding. They yielded p values of < 0.01 when compared with <i>Rothia dentocariosa</i>, <i>Lactobacillus casei</i>, <i>Actinomyces odontolyticus</i> or <i>Actinomyces naeslundii</i> and p values of < 0.05 when contrasted against <i>Streptococcus mitis</i>, <i>Streptococcus sali-varius</i>, <i>Streptococcus sanguis</i>, <i>Lactobacillus acidophilus</i>, <i>Actinomyces viscosus</i>, or <i>Fuso-bacterium nucleatum</i>. With the exception of L. casei and <i>F. nucleatum</i>, the binding of ¹⁸F by growing and resting cells of the assay bacteria did not vary significantly (p > 0.05). Fluoride-sensitive and resistant cells of <i>S. mutans</i> 6715 and <i>S. salivarius</i> did not differ with respect to the amounts of ¹⁸F that they attracted. Similarly no definitive differences in ¹⁸F binding were detected in various serotypes of <i>S. mutans</i>. The binding of ¹⁸F by the assay bacteria could be saturated, did not require addition of an energy source, occurred equally well at 4–37 °C aerobically or anaerobically and in the presence of 500 μ<i>M</i> sodium azide, sodium arsenate, 2,4-dinitrophenol, or N, Nʹ-dicyclohexylcarbodiimide. The establishment of fluoride deposits in oral bacteria suggests a possible exchange of fluoride among these microorganisms or tooth enamel which may influence dental caries.