AUTHOR=Manome Ayumi , Abiko Yuki , Kawashima Junko , Washio Jumpei , Fukumoto Satoshi , Takahashi Nobuhiro 

TITLE=Acidogenic Potential of Oral Bifidobacterium and Its High Fluoride Tolerance

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.01099

DOI=10.3389/fmicb.2019.01099

ISSN=1664-302X

ABSTRACT=<p><italic>Bifidobacterium</italic> is frequently detected in early childhood caries and white spot lesions, indicating that it is a novel caries-associated bacterium. <italic>Bifidobacterium</italic> is known to possess a unique metabolic pathway, the “bifid shunt,” which might give it cariogenic potential by increasing its acid production. Thus, we evaluated the acid-producing activity of <italic>Bifidobacterium</italic> and its sensitivity to fluoride, a caries preventive reagent. <italic>Bifidobacterium longum</italic>, <italic>Bifidobacterium dentium</italic>, and <italic>Streptococcus mutans</italic> were used. Acid-producing activity was measured using a pH-stat in the absence and presence of fluoride under anaerobic conditions. Furthermore, metabolomic analysis was performed to elucidate the mechanism underlying the inhibitory effects of fluoride. The acid production of <italic>Bifidobacterium</italic> at pH 5.5 was as high as that seen at pH 7.0, indicating that <italic>Bifidobacterium</italic> has high cariogenic potential, although it produced less acid than <italic>S. mutans</italic>. In addition, <italic>Bifidobacterium</italic> produced acid in the absence of extracellular carbohydrates, suggesting that it can store intracellular polysaccharides. <italic>Bifidobacterium</italic> produced more acid from lactose than from glucose. <italic>Bifidobacterium</italic> mainly produced acetate, whereas <italic>S. mutans</italic> mainly produced lactate. The 50% inhibitory concentration (IC<sub>50</sub>) of fluoride for acid production was 6.0–14.2 times higher in <italic>Bifidobacterium</italic> than in <italic>S. mutans</italic>. Fluoride inhibited enolase in the glycolysis, resulting in the intracellular accumulation of 3-phosphoenolpyruvate, glucose 6-phosphate, and erythrose 4-phosphate. However, the bifid shunt provides a bypass pathway that can be used to produce acetate, suggesting that <italic>Bifidobacterium</italic> is able to metabolize carbohydrates in the presence of fluoride. It is suggested that its exclusive acetate production contributes to the pathogenesis of dental caries.</p>