Changes in aac(6′)-Ib-cr Prevalence and Fluoroquinolone Resistance in Nosocomial Isolates of Escherichia coli Collected from 1991 through 2005

Clinical isolates of Escherichia coli collected from 1991 through 2005 at a tertiary-care center were studied for qnr and aac(6')-Ib-cr genes. Isolates bearing aac(6')-Ib-cr emerged in 1998, coinciding with an increase in ciprofloxacin resistance. The presence of aac(6')-Ib-cr was multiclonal and was associated with the presence of extended-spectrum beta-lactamases.