title: Substrate specificity of the OqxAB multidrug resistance pump in Escherichia coli and selected enteric bacteria.
abstract: OBJECTIVE
  A plasmid-encoded multidrug efflux pump, OqxAB, identified in Escherichia coli of porcine origin, was tested for substrate specificity against selected antibiotics, detergents and disinfectants. The ability of horizontal transfer to food-borne pathogens of the Enterobacteriaceae family was also investigated.
  
  
  METHODS
  The MICs of selected substrates were determined with a broth dilution assay using two isogenic E. coli strains, except for the presence of the oqxAB operon. A derivative of the plasmid encoding OqxAB (pOLA52) was constructed and horizontal transfer to Salmonella Typhimurium, Klebsiella pneumoniae, Kluyvera sp. and Enterobacter aerogenes was investigated. The effect of the presence of the OqxAB pump on susceptibility for selected compounds was investigated using broth dilution assays.
  
  
  RESULTS
  The OqxAB pump conferred antimicrobial resistance or reduced susceptibility towards a variety of substrates in E. coli. These included animal growth promoters, antimicrobials, disinfectants and detergents. pOLA52 could readily be transferred to enterobacterial pathogens. Transconjugants showed reduced susceptibility towards chloramphenicol, ciprofloxacin and olaquindox.
  
  
  CONCLUSIONS
  The plasmid-encoded OqxAB pump has a wide substrate specificity and can be transferred between Enterobacteriaceae conferring reduced susceptibility to a multitude of substrates. These results could indicate some dependence on the outer membrane proteins present in the different species.
authors.affiliation: Department of Microbiology, Institute of Biology, University of Copenhagen, Sølvgade 83H, 1307 Copenhagen K, Denmark. hestbjerg@bi.ku.dk
authors.forename: Lars Hestbjerg
authors.initials: LH
authors.lastname: Hansen
authors.forename: Lars Bogø
authors.initials: LB
authors.lastname: Jensen
authors.forename: Heidi Iskou
authors.initials: HI
authors.lastname: Sørensen
authors.forename: Søren Johannes
authors.initials: SJ
authors.lastname: Sørensen
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000891:Anti-Infective Agents, Local / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology; D004202:Disinfectants / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D004755:Enterobacteriaceae / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D022761:Gene Transfer, Horizontal; D006133:Growth Substances / Q000494:pharmacology; D008826:Microbial Sensitivity Tests; D010957:Plasmids / Q000235:genetics; D011810:Quinoxalines / Q000494:pharmacology*; D013379:Substrate Specificity
chemical_list: D000900:Anti-Bacterial Agents; D000891:Anti-Infective Agents, Local; D001426:Bacterial Proteins; D003902:Detergents; D004202:Disinfectants; D029968:Escherichia coli Proteins; D006133:Growth Substances; D011810:Quinoxalines; C013168:olaquindox