Broader distribution of plasmid-mediated quinolone resistance in the United States.

The plasmid-encoded quinolone resistance gene qnrA confers low-level quinolone resistance, facilitating selection of higher-level resistance. Epidemiologic surveys for qnrA were extended to isolates of Enterobacter spp. and to quinolone-susceptible Enterobacteriaceae. Two (10%) of 20 ceftazidime-resistant quinolone-susceptible Klebsiella pneumoniae strains carried the gene, as did 12 (17%) of 71 ceftazidime-resistant Enterobacter strains from across the United States. One of these Enterobacter isolates was quinolone susceptible. Thus, qnrA is present in quinolone-resistant and quinolone-susceptible Enterobacter and Klebsiella strains in the United States.