Fluoride resistance in Streptococcus mutans: a mini review

Abstract

For decades, fluoride has been used extensively as an anti-caries agent. It not only protects dental hard tissue, but also inhibits bacterial growth and metabolism. The antimicrobial action of fluoride is shown in three main aspects: the acidogenicity, acidurance, and adherence to the tooth surface. To counteract the toxic effect of fluoride, oral bacteria are able to develop resistance to fluoride through either phenotypic adaptation or genotypic changes. Strains that acquire fluoride resistance through the latter route show stable resistance and can usually resist much higher fluoride levels than the corresponding wild-type strain. This review summarizes the characteristics of fluoride-resistant strains and explores the mechanisms of fluoride resistance, in particular the recent discovery of the fluoride exporters. Since the fluoride resistance of the cariogenic bacterium Streptococcus mutans has been studied most extensively, this review mainly discusses the findings related to this species.

Keywords: Fluoride; Streptococcus mutans; antimicrobial resistance; dental caries.

Figure 1.

Mechanisms for the antimicrobial effects of fluoride and potential sites involved in the mechanisms of fluoride resistance. FEX, fluoride exporters; ARG, arginine; ADS, arginine dehydrolase system; PPi, inorganic pyrophosphate; PPase, pyrophosphatase; Pi, inorganic phosphate; PEP, phosphoenolpyruvate. Red arrows indicate the inhibitory effect of fluoride on the enzymes. Red dashed boxes indicate sites which are potentially involved in fluoride resistance. F-ATPase and enolase are involved in both the antimicrobial action of fluoride and the potential mechanisms of fluoride resistance.