Characteristics of Plasmid-Mediated Quinolone Resistance Genes in Extended-Spectrum Cephalosporin-Resistant Isolates of Klebsiella pneumoniae and Escherichia coli in Korea

Background: Quinolone resistance is frequently associated with extended-spectrum cephalosporin resistance in Enterobacteriaceae. Methods: The characteristics of plasmid-mediated quinolone resistance (PMQR) genes [qnr genes, aac(6′)-Ib-cr and qepA] in clinical isolates of Klebsiella pneumoniae and Escherichia coli resistant to extended-spectrum cephalosporin were studied. Results: 5 and 4 of 95 E. coli isolates but 46 (86/187) and 6% (12/187) of K. pneumoniae had qnr and aac(6′)-Ib-cr, respectively, and 8 K. pneumoniae contained both genes.qepA was not identified. qnrB, especially qnrB4, was the predominant qnr subtype in K. pneumoniae [94 (88 qnrB of 94 qnr) and 88% (77 qnrB4 of 88 qnrB), respectively], and presence of qnrB4 was closely related with DHA-1 β-lactamase (99%). However, K. pneumoniae isolates with qnrB4 and bla DHA-1 were clonally diverse. β-Lactamases produced by PMQR-containing isolates were variable: CMY-1, CTX-M-14, CTX-M-15, DHA-1, OXA type, SHV-2a, and SHV-12. Conclusion: PMQR genes are widely distributed among clinical isolates of K. pneumoniae, and qnrB4 associated with bla DHA-1 was the most common PMQR gene in Korea.