Prevalence in the United States of aac(6 ′ ) - Ib - cr Encoding a Ciprofloxacin-Modifying Enzyme

Abstract

Among 313 Enterobacteriaceae from the United States with a ciprofloxacin MIC of ≥0.25 μg/ml and reduced susceptibility to ceftazidime, aac(6 ′ )-Ib was present in 50.5% of isolates, and of these, 28% carried the cr variant responsible for low-level ciprofloxacin resistance. aac(6 ′ )-Ib-cr was geographically widespread, stable over time, most common in Escherichia coli , equally prevalent in ciprofloxacin-susceptible and -resistant strains, and not associated with qnr genes.