Prevalence of aac(6')-Ib-cr plasmid-mediated and chromosome-encoded fluoroquinolone resistance in Enterobacteriaceae in Italy.

The spread of aac(6')-Ib-cr plasmid-mediated quinolone resistance determinants was evaluated in 197 enterobacterial isolates recovered in an Italian teaching hospital. The aac(6')-Ib-cr gene was found exclusively in Escherichia coli strains. The gene was located on a plasmid which presented additional ESBL genes. Most of the clinical strains were clonally related and displayed three point mutations at the topoisomerase level which conferred high resistance to fluoroquinolones.