| Summary: | Abstract Background The rate of fluoroquinolone (FQ) resistance among carbapenem-resistant Klebsiella pneumoniae (CRKP) is high. The present study aimed to investigate the distribution of fluoroquinolone resistance determinants in clinical CRKP isolates associated with bloodstream infections (BSIs). Results A total of 149 BSI-associated clinical CRKP isolates collected from 11 Chinese teaching hospitals from 2015 to 2018 were investigated for the prevalence of fluoroquinolone resistance determinants, including plasmid-mediated quinolone resistance (PMQR) genes and spontaneous mutations in the quinolone resistance-determining regions (QRDRs) of the gyrA and parC genes. Among these 149 clinical CRKP isolates, 117 (78.5%) exhibited resistance to ciprofloxacin. The GyrA substitutions (Ser83 → IIe/Phe) and (Asp87 → Gly/Ala) were found among 112 (75.2%) of 149 isolates, while the substitution (Ser80 → IIe) of ParC was found in 111 (74.5%) of the 149 isolates. In total, 70.5% (105/149) of the CRKP isolates had at least two mutations within gyrA as well as a third mutation in parC. No mutations in the QRDRs were found in 31 ciprofloxacin susceptible CRKP isolates. Eighty-nine (56.9%) of 149 were found to carry PMQR genes including qnrS1 (43.0%), aac(6′)-Ib-cr (16.1%), qnrB4 (6.0%), qnrB2 (2.7%), and qnrB1 (1.3%). Nine isolates contained two or more PMQR genes, with one carrying four [aac(6′)-Ib-cr, qnr-S1, qnrB2, and qnrB4]. The co-existence rate of PMQR determinants and mutations in the QRDRs of gyrA and parC reached 68.5% (61/89). Seventy-four (83.1%, 74/89) PMQR-positive isolates harbored extended-spectrum beta-lactamase (ESBL)-encoding genes. Multilocus sequence typing (MLST) analysis demonstrated that the ST11 was the most prevalent STs in our study. Conclusions Mutations in the QRDRs of gyrA and parC were the key factors leading to the high prevalence of fluoroquinolone resistance among BSI-associated CRKP. The co-existence of PMQR genes and mutations in the QRDRs can increase the resistance level of CRKP to fluoroquinolones in clinical settings. ST11 CRKP isolates with identical QRDR substitution patterns were found throughout hospitals in China.
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