Abstract
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
≥ 4 µg/mL) to the following fluoroquinolones: ofloxacin, levofloxacin, sparfloxacin, and trovafloxacin. These isolates were cross-resistant to chloramphenicol (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 electrophoresis (PFGE) revealed
a high diversity among the genomes of these isolates and indicated that clonal spread was not responsible for the prevalence of ciprofloxacin 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 mutations 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 (S83L) 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 asparagine (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-level resistance to quinolones in clinical
E. coli
isolates were associated with mutations at hot spots, codon 83 and 87 in GyrA and followed by subsequent mutation in either codon 80 and/or
84 in ParC.