JAC Advance Access published online on May 24, 2007
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkm167
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Substrate specificity of the OqxAB multidrug resistance pump in Escherichia coli and selected enteric bacteria
1 Department of Microbiology, Institute of Biology, University of Copenhagen, Sølvgade 83H, 1307 Copenhagen K, Denmark 2 Unit for Antimicrobial Resistance, The National Food Institute, DTU, Bülowsvej 27, DK-1790 Copenhagen V, Denmark
Received 24 January 2007; returned 4 February 2007; revised 18 April 2007; accepted 20 April 2007
* Corresponding author. Tel: +45-35322053; Fax: +45-35322040; E-mail: hestbjerg{at}bi.ku.dk
Objectives: 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.
Key Words: multidrug efflux pumps , antibiotic resistance , growth promoters , disinfectants , detergents
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