Acetaldehyde production from ethanol by oral streptococci.

Alcohol is a well documented risk factor for upper digestive tract cancers. It has been shown that acetaldehyde, the first metabolite of ethanol is carcinogenic. The role of microbes in the production of acetaldehyde to the oral cavity has previously been described in several studies. In the present study, the aim was to investigate the capability of viridans group streptococci of normal oral flora to produce acetaldehyde in vitro during ethanol incubation. Furthermore, the aim was to measure the alcohol dehydrogenase (ADH) activity of the bacteria. Eight clinical strains and eight American Type Culture Collection (ATCC) strains of viridans group streptococci were selected for the study. Bacterial suspensions were incubated in two different ethanol concentrations, 11 mM and 1100 mM and the acetaldehyde was measured by gas chromatography. ADH-activity was measured by using a sensitive spectroscopy. The results show significant differences between the bacterial strains regarding acetaldehyde production capability and the detected ADH-activity. In particular, clinical strain of Streptococcus salivarius, both clinical and culture collection strains of Streptococcus intermedius and culture collection strain of Streptococcus mitis produced high amounts of acetaldehyde in 11 mM and 1100 mM ethanol incubation. All these four bacterial strains also showed significant ADH-enzyme activity. Twelve other strains were found to be low acetaldehyde producers. Consequently, our study shows that viridans group streptococci may play a role in metabolizing ethanol to carcinogenic acetaldehyde in the mouth. The observation supports the concept of a novel mechanism in the pathogenesis of oral cancer.