A MATE family multidrug efflux transporter pumps out fluoroquinolones in Bacteroides thetaiotaomicron

We cloned a gene, bexA, that codes for a multidrug efflux transporter from the chromosomal DNA of Bacteroides thetaiotaomicron ATCC 29741 by using an Escherichia coli Delta acrAB Delta acrEF mutant as a host. Although the ini tial recombinant construct contained other open reading frames, the presenc e of bexA alone was sufficient to confer to the E. coli host elevated level s of resistance to norfloxacin, ciprofloxacin, and ethidium bromide. Disrup tion of bexA in B. thetaiotaomicron made the strain more susceptible to nor floxacin, ciprofloxacin, and ethidium bromide, showing that this gene is ex pressed in this organism and functions as a multidrug efflux pump. The dedu ced BexA protein sequence was homologous to the protein sequence of Vibrio parahaemolyticus NorM, a multidrug efflux transporter, and thus, BexA belon gs to the multidrug and toxic compound extrusion (MATE) family.