Bifacial biological effects of ethanol: acetaldehyde production by oral species and the antibacterial effects of ethanol against these bacteria.

Many previous studies have focused on the acetaldehyde produced from ethanol by oral bacteria as a risk factor for oral cancer. Most of these studies involved low ethanol concentrations (ca. 10 mM), but oral bacteria are exposed to a wide range of ethanol concentrations (100-10,000 mM) when alcoholic beverages are consumed. In contrast, ethanol is widely used at high concentrations (> 5,000 mM) as an antiseptic/disinfectant, suggesting that ethanol has bifacial biological effects; i.e. it acts as both a metabolic substrate for bacterial acetaldehyde production and an antimicrobial agent. We examined the acetaldehyde production from ethanol by oral streptococci and the effects of ethanol exposure on the growth and viability of these bacteria at a wide range of ethanol concentrations (10-10,000 mM). Acetaldehyde production was the highest at an ethanol concentration of 2,000 mM (2.1-48-fold higher than that seen at an ethanol concentration of 10 mM). Bacterial growth was inhibited by > 1,000 mM of ethanol, and the bacteria did not seem viable in the presence of > 5,000 mM of ethanol, although they still produced acetaldehyde. Ethanol has bifacial biological effects, and the concentration ranges of these effects overlap.