Acetaldehyde production and other ADH-related characteristics of aerobic bacteria isolated from hypochlorhydric human stomach

Background: Acetaldehyde is a known local carcinogen in the digestive tract in humans. Bacterial overgrowth in the hypochlorhydric stomach enhances pr oduction of acetaldehyde from ethanol in vivo after alcohol ingestion. Ther efore, microbially produced acetaldehyde may be a potential risk factor for alcohol-related gastric and cardiac cancers. This study was aimed to inves tigate which bacterial species and/or groups are responsible for acetaldehy de formation in the hypochlorhydric human stomach and to characterize their alcohol dehydrogenase (ADH) enzymes. Methods: After 7 days of treatment with 30 mg of lansoprazole twice a day, a gastroscopy was performed on eight volunteers to obtain hypochlorhydric g astric juice. Samples were cultured and bacteria were isolated and identifi ed; thereafter, their acetaldehyde production capacity was measured gas chr omatographically by incubating intact bacterial suspensions with ethanol at 37 degreesC. Cytosolic ADH activities, K-m values, and protein concentrati on were determined spectrophotometrically. Results: Acetaldehyde production of the isolated bacterial strains (n = 51) varied from less than 1 to 13,690 nmol of acetaldehyde/10(9) colony-formin g units/hr. ADH activity of the strains that produced more than 100 nmol of acetaldehyde/10(9) colony-forming units/hr (n = 23) varied from 3.9 to 125 3 nmol of nicotinamide adenine dinucleotide per minute per milligram of pro tein, and K-m values for ethanol ranged from 0.65 to 116 mM and from 0.5 to 3.1 M (high K-m). There was a statistically significant correlation (r = 0 .64, p < 0.001) between ADH activity and acetaldehyde production from ethan ol in the tested strains. The most potent acetaldehyde producers were Neiss eria and Rothia species and Streptococcus salivarius, whereas nearly all St omatococcus, Staphylococcus, and other Streptococcus species had a very low capacity to produce acetaldehyde, Conclusions: This study demonstrated that certain bacterial species or grou ps that originate from the oral cavity are responsible for the bulk of acet aldehyde production in the hypochlorhydric stomach. These findings provide new information with the respect to the local production of carcinogenic ac etaldehyde in the upper digestive tract of achlorhydric human subjects.