Molecular epidemiology and mutations at gyrA and parC genes of ciprofloxacin-resistant Escherichia coli isolates from a Taiwan Medical Center

Sixty-five ciprofloxacin-resistant clinical Escherichia coli isolates were collected from a Taiwan Medical Center from December 1998 to February 1999. All 65 clinical isolates were resistant (MICs greater than or equal to 4 m ug/mL) to the following fluoroquinolones: ofloxacin, levofloxacin, sparflox acin, and trovafloxacin. These isolates were cross-resistant to chloramphen icol (65 isolates, 100%), tetracycline (65 isolates, 100%), cefuroxime (64 isolates, 98.5%), ampicillin (57 isolates, 87.7%), gentamicin (53 isolates, 81.5%), and cephalothin (24 isolates, 36.9%). Pulsed-field gel electrophor esis (PFGE) revealed a high diversity among the genomes of these isolates a nd indicated that clonal spread was not responsible for the prevalence of c iprofloxacin resistance in the hospital. Sequencing of the polymerase chain reaction (PCR) amplified products of the quinolone resistance determining regions (QRDRs) of gyrA and parC showed that all isolates carrying double m utations in gyrA at codon 83 and 87 and at least one parC mutation at codon 80 and/or 84. The mutation at codon 83 of GyrA from serine to leucine (S83 L) was present in all the clinical isolates. The most prevalent pattern was the S83L mutation and the mutation at codon 87 from an aspartate to an asp aragine (D87N) of GyrA plus a mutation from a serine to an isoleucine (S80I ) at codon 80 of ParC (63.2%). This indicated that the presence of high-lev el resistance to quinolones in clinical E. coli isolates were associated wi th mutations at hot spots, codon 83 and 87 in GyrA and followed by subseque nt mutation in either codon 80 and/or 84 in ParC.