Effects of a plasmid-encoded qnrA1 determinant in Escherichia coli strains carrying chromosomal mutations in the acrAB efflux pump genes.

The qnrA1 gene was cloned into a plasmid vector and transformed into Escherichia coli strains carrying chromosomal mutations in the acrAB drug efflux system. In acrAB-deleted strains, and in strains overexpressing acrAB, viable qnrA conferred higher MIC levels (at least a 32-fold increase) for fluoroquinolones than were observed in the parent strains.