Resistance characteristics and mechanism of carbapenem-resistant Klebsiella pneumoniae to quinolones

  Background  There is a lack of research about Carbapenem-resistant Klebsiae pneumoniae (CRKP) resistance to quinolones and citafloxacin (a new generation of quinolones) in China.

  Objective  To investigate the resistance characteristics and mechanisms of carbapenem-resistant Klebsiella pneumoniae (CRKP) to quinolones.

  Methods  Twenty-nine clinical isolates of non-repetitive carbapenem-resistant Klebsiella pneumoniae were collected from Chinese PLA General Hospital. The sensitivity of CRKP to quinolones and the effect of efflux pump inhibitors on the resistance of CRKP were detected by broth microdilution method. The in vitro antibacterial activity of sitafloxacin combined with other antibacterial agents against CRKP was detected by checkerboard method. QRDR (quinolone resistance-determining region) mutations were detected by Sanger sequencing. Plasmid-mediated quinolone resistance gene (PMQR), efflux pump, and multilocus sequence typing (MLSP) were detected by whole genome sequencing.

  Results  The resistance rates of 29 CRKP strains to sitafloxacin, moxifloxacin, and ciprofloxacin were 90%, 3%, and 93%, respectively. The MIC₅₀ of sitafloxacin was 4 times that of moxifloxacin and 8 times that of ciprofloxacin. The susceptibility rates of sitafloxacin to bla_KPC, bla_NDM, and bla_OXA-48 positive CRKP were 4.7%, 66.6%, and 0, respectively. The results of antimicrobial synergy study showed that synergistic, partial synergistic and additive effects of sitafloxacin combined with colistin, eravacycline, and tigecycline to the CRKP were 70%, 20%, and 6%, respectively. The QRDR mutation rates of bla_KPC, bla_NDM, and bla_OXA-48 positive CRKP were 95%, 0, and 100%, respectively. The rate of plasmid-mediated quinolone resistance gene (PMQR) was 83%. RND efflux pumps were commonly carried in CRKP strains. Efflux pump inhibitors increased the susceptibility rate of CRKP to sitafloxacin from 10% to 83%, and reduced the resistance rate from 90% to 7%. All the dominant ST types were bla_KPC-2 positive strains.

  Conclusion  CRKP has a high resistance rate to quinolones. Sitafloxacin and colistin have the best synergistic effect. QRDR mutation and overexpression of efflux pump are the main resistance mechanisms of CRKP to quinolones, while the NDM-producing CRKP has no mutation in QRDR and is sensitive to quinolones. ST11 bla_KPC-2 positive strains are the predominant strains in our hospital.