Substrate specificity of the OqxAB multidrug resistance pump in Escherichia coli and selected enteric bacteria

<st>Objectives</st> A plasmid-encoded multidrug efflux pump, OqxAB, identified in <it>Escherichia coli</it> 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. <st>Methods</st> The MICs of selected substrates were determined with a broth dilution assay using two isogenic <it>E</it>. <it>coli</it> strains, except for the presence of the <it>oqxAB</it> operon. A derivative of the plasmid encoding OqxAB (pOLA52) was constructed and horizontal transfer to <it>Salmonella</it> Typhimurium<it>, Klebsiella pneumoniae</it>, <it>Kluyvera</it> sp. and <it>Enterobacter aerogenes</it> was investigated. The effect of the presence of the OqxAB pump on susceptibility for selected compounds was investigated using broth dilution assays. <st>Results</st> The OqxAB pump conferred antimicrobial resistance or reduced susceptibility towards a variety of substrates in <it>E</it>. <it>coli</it>. 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. <st>Conclusions</st> 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.