Tn. Phan et al., Sensitization of Actinomyces naeslundii and Streptococcus sanguis in biofilms and suspensions to acid damage by fluoride and other weak acids, ARCH MICROB, 174(4), 2000, pp. 248-255
Fluoride and other weak acids, such as benzoate, indomethacin, salicylate a
nd sorbate, were found to be sensitizers for acid killing of cells of Actin
omyces naeslundii ATCC 19246 and Streptococcus sanguis NCTC 10904 in suspen
sions or in mono-organism biofilms on glass slides. These bacteria are amon
g the more acid-sensitive organisms from dental plaque and were killed when
acidified to pH values between 3.5 and 4.0. Biofilm cells were more resist
ant than cells in suspensions, especially in terms of the fraction of the i
nitial population surviving acidification. The mechanism for sensitization
to acid killing by fluoride and the other weak acids involved enhanced tran
smembrane transport of protons, reflected by increases in measured proton p
ermeabilities of the cells. Thus, the weak acids thwarted the functions of
F(H+)-ATPases in extruding protons and protecting cells against acid damage
. Fluoride sensitization of-biofilms or cells in suspensions to acid damage
occurred rapidly. There was a delay in sensitization of biofilms by indome
thacin and higher molecular weight acids Which was interpreted in terms of
diffusion limitation of sensitizer penetration. Overall, it seemed that wea
k-acid sensitization to acid killing is a general phenomenon that occurs no
t just for oral bacteria but also for organisms in food, soil, and other ac
idified environments.