Mutations in DNA Gyrase and Topoisomerase IV in Ciprofloxacin-Nonsusceptible Extended-Spectrum -Lactamase-Producing Escherichia coli and Klebsiella pneumoniae.

Background: We investigated mutations in the quinolone resistance-determining region (QRDR) of ciprofloxacinnonsusceptible extended-spectrum -lactamase (ESBL)-producing Escherichia coli and Klebsiella pneumoniae by a statistical analysis.

Methods: We collected 97 clinical isolates of ciprofloxacin-nonsusceptible ESBL-producing E. coli (55 strains) and K. pneumoniae (42 strains) from a tertiary-care university hospital in Seoul, Republic of Korea, between 2006 and 2008. The QRDR of the gyrA, gyrB, parC, and parE genes were amplified by PCR and sequenced.

Results: Most E. coli isolates (53/55; 96.4%) with a minimum inhibitory concentration of ≥ 64 mg/L against ciprofloxacin had double mutations in gyrA (Ser-83Leu and Asp-87Asn) and at least one mutation in parC (Ser-80 Ile or Glu-84Val), with or without one in parE. Fifty E. coli (90.9%) isolates had a mutation in parE, of which Ile-529Leu (70.9%) was the most frequent. However, we could not find statistically significant variables in increasing ciprofloxacin resistance in E. coli isolates. Thirty-six K. pneumoniae isolates (36/42; 85.7%) had at least one mutation in gyrA, gyrB, or parC, and the mutation in gyrA might have been associated with plasmid-mediated quinolone-resistance (PMQR). Ser-80Ile in parC and aac(6')-Ib-cr in the K. pneumoniae isolates were significantly associated with an increased MIC of ciprofloxacin by ordinal logistic regression analysis.

Conclusions: The Ser-80Ile in parC and aac(6')-Ib-cr in K. pneumoniae are supposed to play an important role in increased ciprofloxacin resistance, but statistically significant variables could not be found in E. coli isolates in the present study.