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Abstract
Acetaldehyde is known to be carcinogenic and produced by oral bacteria. Thus, bacterial acetaldehyde production might contribute to oral cancer. Therefore, we examined bacterial acetaldehyde production from ethanol and glucose under various conditions mimicking the oral cavity and clarified the metabolic pathways responsible for bacterial acetaldehyde production. Streptococcus mitis, S. salivarius, S. mutans, Neisseria mucosa and N. sicca were used. The bacterial metabolism was conducted at pH 5.0–8.0 under aerobic and anaerobic conditions. The production of acetaldehyde and organic acids was measured with gas chromatography and HPLC, respectively. Bacterial enzymes were also assessed. All of the bacteria except for S. mutans exhibited their greatest acetaldehyde production from ethanol at neutral to alkaline pH under aerobic conditions. S. mutans demonstrated the greatest acetaldehyde from glucose under anaerobic conditions, although the level was much lower than that from ethanol. Alcohol dehydrogenase and NADH oxidase were detected in all of the bacteria. This study revealed that oral indigenous bacteria, Streptococcus and Neisseria can produce acetaldehyde, and that such acetaldehyde production is affected by environmental conditions. It was suggested that alcohol dehydrogenase and NADH oxidase are involved in ethanol-derived acetaldehyde production and that the branched-pathway from pyruvate is involved in glucose-derived acetaldehyde production.
Highlights
Many epidemiological studies have reported that chronic and heavy alcohol consumption, as well as poor oral hygiene, are strongly correlated with oral cancer[1,2,3,4]
S. salivarius, S. mitis, N. mucosa, and N. sicca exhibited greater acetaldehyde production from ethanol under aerobic conditions than under anaerobic conditions (Fig. 1), indicating that aerobic conditions are preferable for acetaldehyde production from ethanol
S. salivarius and S. mitis produced acetaldehyde from glucose, the amounts of acetaldehyde produced were much smaller than those produced from ethanol (Fig. 2), confirming that ethanol is the preferred substrate for acetaldehyde production, as reported previously[14]
Summary
Many epidemiological studies have reported that chronic and heavy alcohol consumption, as well as poor oral hygiene, are strongly correlated with oral cancer[1,2,3,4]. The findings described above suggest that the accumulation of oral bacteria due to poor oral hygiene might increase bacterial acetaldehyde production and subsequently contribute to the development of oral cancer. Oral bacteria, such as Neisseria, Streptococcus, Actinomyces, and Prevotella species, and Candida species www.nature.com/scientificreports/. We aimed to examine acetaldehyde production by representative examples of the dominant indigenous acetaldehyde-producing bacteria in the oral cavity; i.e., Streptococcus and Neisseria species, and the effects of oral environmental factors; i.e., pH and the concentrations of oxygen and metabolic substrates, on the metabolic activity of such bacteria. We attempted to suggest the metabolic properties of bacterial acetaldehyde production by detecting the enzymes involved in acetaldehyde production as well as the associated metabolic end-products
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