Impact of plasmid-mediated quinolone resistance genes on the quinolone resistance in clinical isolates and cloned strains

Abstract

Impact of Plasmid-Mediated Quinolone Resistance Genes on the Quinolone Resistance in Clinical Isolates and Cloned Strains

Division of Infectious Diseases and Clinical Microbiology1, College of Medicine, Hanyang University Division of Infectious Diseases, College of Medicine, Kacheon University2 Hyunjoo Pai, Mi-Ran Seo, Tae Yeal Choi1, Yoon Soo Park2

Background : Aac(6`)-Ib-cr, a muntant of aminoglycosde modifying enzyme gene was recently known to confer a low level resistance to ciprofloxacin. Obiectives : The objectives of the study are to observe the prevalence of aac(6`)-b-crdeterminant in clinical isolates of Enterobacteriaceae producing ESBL or plasmid-mediated AmpC β- lactamases (PABL) and to identify the association of aac(6`)-Ib-cr with qnr. Methods : the presence of aas(6`)-Ib-cr was screened for 77 isolates of E.coli and 181 isolates of K.pneumoniae producing ESBL or PABL collected from different institution during the period from 1998 to 2007 by the PCR and restriction enzyme analyses. qnrB2, qnrB4, aac(6)-Ib-cr was cloned and the E. coliDH10B containing aac(6`)-Ib-cr and each of qnrB2, B4, or S was constructed. The MICs of fluoroquinolones for clinical isolates and cloned strains were measured. Results : No clinical isolates of E.coli producing ESBL or PABL harbored aac(6`)-Ib-cr. However, aac(6`)-Ib was prevalent in K. pneumoniae with ESBL or PABL: 13 of 181 K. pneumoniae harbored aac(6`)-Ib-cr (7.2%), and 3 of them contained both the qnrB4 and aac(6`)-Ib-cr. Clinical isolates containing two kind of plasmid-mediated quinolone resistance genes showed higher level of resistance to ciprofloxacin, ofloxacin, levofloxacin and moxifloxacin. However, E. coli DH10B containing natural plasmid with aac(6`)-Ib-cr and each of cloned PBCSK(+) qnrB2, B4, and S showed 2-fold increase of ciprofloxacin compared to the strain with qnr gene alone. Conclusion : The results suggest widespread distribution of resistant plasmids encoding aac(6`)-Ib-cr in clinical isoates of K. pneumoniae producing ESBL or PABL. The clinical isolates of K. pneumoniae containing both aac(6`)-Ib-cr and various qnr genes showed high level resistance to fluoroquinolones, but transfer of both genes into E. coli DH10B resulted 2-fold increase of ciprofloxacin MIC than that with qnr B or S.