ACETALDEHYDE PRODUCTION AND METABOLISM BY HUMAN INDIGENOUS AND PROBIOTIC LACTOBACILLUS AND BIFIDOBACTERIUM STRAINS

Many human gastrointestinal facultative anaerobic and aerobic bacteria possess alcohol dehydrogenase (ADH) activity and are therefore capable of oxidizing ethanol to acetaldehyde. We examined whether human gastrointestinal lactobacilli (three strains), bifidobacteria (five strains) and probiotic Lactobacillus GG ATCC 53103 are also able to metabolize ethanol and acetaldehyde in vitro. Acetaldehyde production by bacterial suspensions was determined by gas chromatography after a 1-h incubation with 22 mM ethanol. To determine the acetaldehyde consumption, the suspensions were incubated with 50 microM or 500 microM acetaldehyde as well as with 500 microM acetaldehyde and 22 mM ethanol, i.e. under conditions resembling those in the human colon after alcohol intake. The influence of growth media and bacterial concentration on the ability of lactobacilli to metabolize acetaldehyde and to produce acetate from acetaldehyde were determined. ADH and aldehyde dehydrogenase (ALDH) activities were determined spectrophotometrically. Neither measurable ADH nor ALDH activities were found in aerobically grown Lactobacillus GG ATCC 53103 and Lactobacillus acidophilus ATCC 4356 strains. All the lactobacilli and bifidobacteria strains revealed a very limited capacity to oxidize ethanol to acetaldehyde in vitro. Lactobacillus GG ATCC 53103 had the highest acetaldehyde-metabolizing capacity, which increased significantly with increasing bacterial concentrations. This was associated with a marked production of acetate from acetaldehyde. The type of the growth media had no effect on acetaldehyde consumption. Addition of ethanol to the incubation media diminished the acetaldehyde-metabolizing capacity of all strains. However, in the presence of ethanol, Lactobacillus GG ATCC 53103 still demonstrated the highest capacity for acetaldehyde metabolism of all strains. These data suggest a beneficial impact of Lactobacillus GG ATCC 53103 on high gastrointestinal acetaldehyde levels following alcohol intake. The possible clinical implications of this finding remain to be established in in vitro studies.