Prevalence of plasmid-mediated quinolone resistance genes in Klebsiella pneumoniae strains in pediatrics in China

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Objective To investigate the prevalence of plasmid-mediated quinolone resistance (PMQR) genes among clinical isolates of Klebsiella pneumoniae (K.pneumoniae) in pediatrics. Methods A total of 131 non-duplicate clinical isolates of K. pneumoniae were collected in the Affiliated Children′s Hospital of Capital Institute of Pediatrics from 2010 to 2012. PMQR genes [qnrA, qnrB, qnrS, aac(6′)-Ⅰb-cr and qepA], mutations in the quinolone resistance-determining region (QRDR) and extended spectrum β-lactamases (ESBLs) genes in those strains were analyzed by PCR. Minimum inhibitory concentrations (MIC) of different antibiotics against those K. pneumoniae strains were determined by broth microdilution method and E-test according to the guidelines issued by the Clinical and Laboratory Standards Institute (CLSI). Transferability of the PMQR genes was examined by conjugation test with the sodiumazide-resistant Escherichia coli J53. Results Among the 131 isolates, 9.92% were resistant to quinolone and 30.5% were positive for PMQR genes, including 6.87% harboring qnrB gene, 22.9% harboring qnrS gene and 4.58% harboring aac(6′)-Ⅰb-cr gene. Neither qnrA-positive nor qepA-positive strain was detected. Among these PMQR genes-positive isolates, 90% were ESBLs-producing strains and two presented mutations in gyrA and parC genes. Conjugation test showed that these PMQR genes could be transferred horizontally and the ciprofloxacin resistance increased 2 to 32 folds in transconjugants. Conclusion This study indicates that the PMQR gene-carrying rate is high in K. pneumoniae strains isolated in paediatrics in China. Most of the PMQR gene-positive strains are also ESBLs-producing strains. The PMQR genes could be transferred horizontally in bacteria. Key words: Klebsiella pneumoniae; PMQR; ESBLs