Prevalence of Plasmid-Mediated Quinolone Resistance Genes and Ciprofloxacin Resistance in Pediatric Bloodstream Isolates of Enterobacteriaceae over a 9-Year Period

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A total of 279 isolates of Escherichia coli (n = 128) and Klebsiella pneumoniae (n = 151) were obtained from blood samples from children at the Seoul National University Children's Hospital, Seoul, Korea from 1999 to 2007. Five plasmid-mediated quinolone resistance (PMQR) genes, qnrA, qnrB, qnrS, qepA, and aac(6′)-Ib-cr, and the minimal inhibitory concentration (MIC) values for ciprofloxacin were tested for all the strains. Mutations in both gyrA and parC were analyzed in 57 representative strains. Twenty-seven strains (9.7%) had at least 1 of the 5 PMQR genes: qnrB in 20 isolates, qnrS in 1, aac(6′)-Ib-cr in 5, and both qnrB and aac(6′)-Ib-cr in 1 isolate. The overall PMQR prevalence rates tended to increase over time (P = 0.001). The non-susceptibility rate to ciprofloxacin was 11.0% (31/279). PMQR-harboring isolates tended to have increased ciprofloxacin MIC values among both quinolone resistance-determining region (QRDR) mutation-present (P = 0.016) and QRDR mutation-absent isolates (P < 0.001). The increasing prevalence of PMQR genes was associated with increase in quinolone use over time (P < 0.001) and increasing frequency of non-susceptibility to ciprofloxacin (P < 0.001).