title: Ethanol oxidation and acetaldehyde production in vitro by human intestinal strains of Escherichia coli under aerobic, microaerobic, and anaerobic conditions.
abstract: BACKGROUND
  Many human colonic facultative anaerobic and aerobic bacteria are capable of alcohol dehydrogenase (ADH)-mediated ethanol oxidation. In this bacteriocolonic pathway for ethanol oxidation intracolonic ethanol is first oxidized by bacterial ADHs to acetaldehyde, which is further oxidized by either colonic mucosal or bacterial aldehyde dehydrogenases to acetate. The produced acetaldehyde is a highly toxic and carcinogenic agent. This study was aimed to investigate the ethanol oxidation capability and acetaldehyde formation of Escherichia coli IH 50546 and IH 50817. These intestinal E. coli strains expressed either high (IH 50546) or low (IH 50817) ADH activity.
  
  
  METHODS
  Strains were cultured for 48 h on agar plates supplemented with ethanol under aerobic, microaerobic (6% O2), and anaerobic conditions.
  
  
  RESULTS
  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 microM), suggesting ADH-mediated ethanol oxidation. Under microaerobic conditions only IH 50546 was able to oxidize ethanol (ECR, 0.498+/-0.074 mM/h) and to produce acetaldehyde (up to 440+/-76 microM) to significant extents. Under anaerobic conditions both strains fermented glucose to ethanol.
  
  
  CONCLUSIONS
  This study experimentally shows the potential of certain bacteria representing normal human colonic flora to produce acetaldehyde under various atmospheric conditions that may prevail in different parts of the GI tract. This bacterial adaptation may be an essential feature of the bacteriocolonic pathway to produce toxic and carcinogenic acetaldehyde from either endogenous or exogenous ethanol.
authors.affiliation: Research Unit of Alcohol Diseases, University Central Hospital of Helsinki, Finland.
authors.forename: V
authors.initials: V
authors.lastname: Salaspuro
authors.forename: S
authors.initials: S
authors.lastname: Nyfors
authors.forename: R
authors.initials: R
authors.lastname: Heine
authors.forename: A
authors.initials: A
authors.lastname: Siitonen
authors.forename: M
authors.initials: M
authors.lastname: Salaspuro
authors.forename: H
authors.initials: H
authors.lastname: Jousimies-Somer
mesh_terms: D000079:Acetaldehyde / Q000378:metabolism*; D000426:Alcohol Dehydrogenase / Q000378:metabolism*; D001420:Bacteria, Aerobic / Q000201:enzymology / Q000502:physiology; D001421:Bacteria, Anaerobic / Q000201:enzymology / Q000502:physiology; D004755:Enterobacteriaceae / Q000201:enzymology*; D004926:Escherichia coli / Q000201:enzymology*; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation / Q000502:physiology; D006801:Humans; D007413:Intestinal Mucosa / Q000382:microbiology / Q000502:physiology; D010084:Oxidation-Reduction
chemical_list: D000431:Ethanol; D000426:Alcohol Dehydrogenase; D000079:Acetaldehyde