Ethanol oxidation and acetaldehyde production in vitro by human intestinalstrains of Escherichia coli under aerobic, microaerobic, and anaerobic conditions

Background: Many human colonic facultative anaerobic and aerobic bacteria a re capable of alcohol dehydrogenase (ADH)-mediated ethanol oxidation. In th is bacteriocolonic pathway for ethanol oxidation intracolonic ethanol is fi rst oxidized by bacterial ADHs to acetaldehyde, which is further oxidized b y either colonic mucosal or bacterial aldehyde dehydrogenases to acetate. T he produced acetaldehyde is a highly toxic and carcinogenic agent. This stu dy was aimed to investigate the ethanol oxidation capability and acetaldehy de formation of Escherichia coli IH 50546 and IH 50817. These intestinal E. coli strains expressed either high (IH 50546) or low (IH 50817) ADH activi ty. Methods: Strains were cultured for 48 h on agar plates supplemented wit h ethanol under aerobic, microaerobic (6% O-2), and anaerobic conditions. R esults: Under aerobic conditions both E. coli strains oxidized ethanol. The ethanol consumption rates (ECR) were 1.046 +/- 0.025 mM/h and 0.367 +/- 0. 148 mM/h with IH 50546 and IH 50817, respectively. In the case of IH 50546 this was associated with significant acetaldehyde production (418 +/- 13 mu M), suggesting ADH-mediated ethanol oxidation. Under microaerobic conditio ns only IH: 50546 was able to oxidize ethanol (ECR, 0.498 +/- 0.074 mM/h) a nd to produce acetaldehyde (up to 440 +/- 76 mu M) to significant extents. Under anaerobic conditions both strains fermented glucose to ethanol. Concl usions: This study experimentally shows the potential of certain bacteria r epresenting normal human colonic flora to produce acetaldehyde under variou s atmospheric conditions that may prevail in different parts of the GI trac t. This bacterial adaptation may be an essential feature of the bacteriocol onic pathway to produce toxic and carcinogenic acetaldehyde from either end ogenous or exogenous ethanol.