Plasmid-encoded multidrug efflux pump conferring resistance to olaquindox in Escherichia coli.
We report here the first gene-encoded resistance mechanism to the swine growth enhancer olaquindox. The genetic elements involved in resistance to olaquindox were subcloned and sequenced from a conjugative plasmid isolated from Escherichia coli. The subcloned fragment contained two open reading frames, oqxA and oqxB, that are homologous to several resistance-nodulation-cell-division family efflux systems from different species. The putative protein sequences were aligned to both experimentally verified and putative efflux pumps. We show that oqxA and oqxB are expressed in E. coli. Plasmids containing the oqxAB genes yielded high (>128 microg/ml) resistance to olaquindox in E. coli, whereas strains containing the control plasmid showed low resistance to the drug (8 microg/ml). The oqxAB-encoded pump also conferred high (>64 microg/ml) resistance to chloramphenicol. We demonstrate that the subcloned fragment conferred H(+)-dependent ethidium efflux abilities to E. coli strain N43. In addition, we show that the efflux system is dependent on the host TolC outer membrane protein when expressed in E. coli.
Department of Microbiology, University of Copenhagen, Sølvgade 83H, 1307 Copenhagen K, Denmark. hestbjerg@mermaid.molbio.ku.dk
Lars Hestbjerg
LH
Hansen
Elsebetta
E
Johannesen
Mette
M
Burmølle
Anders Hay
AH
Sørensen
Søren J
SJ
Sørensen
D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics; D002701:Chloramphenicol / Q000494:pharmacology; D003001:Cloning, Molecular; D003227:Conjugation, Genetic; D003470:Culture Media; D024881:Drug Resistance, Bacterial / Q000235:genetics; D004734:Energy Metabolism / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000378:metabolism; D004926:Escherichia coli / Q000187:drug effects* / Q000378:metabolism; D029968:Escherichia coli Proteins; D004996:Ethidium / Q000378:metabolism; D006859:Hydrogen / Q000494:pharmacology; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics; D010957:Plasmids / Q000235:genetics*; D011810:Quinoxalines / Q000494:pharmacology*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D003470:Culture Media; D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D011810:Quinoxalines; C073126:tolC protein, E coli; D002701:Chloramphenicol; D006859:Hydrogen; D004996:Ethidium; C013168:olaquindox