Background
The soaring quinolone-resistance rate of Klebsiella pneumoniae, a common pathogen in immunocompromised individuals, has seriously undermined the wide applications of antimicrobials of this class. This study aimed to investigate the emerging key contributors to quinolone-resistance in multidrug resistant K. pneumoniae (MDR-KP) isolates from a clinical setting with continuing point-source infection outbreaks in Shanghai, China.
Results
Between January and March 2017, a total of 34 K. pneumoniae isolates, including 30 carbapenem-resistant K. pneumoniae (CRKP), were selected and characterized from a teaching hospital participating in an ongoing Bacterial Resistance Surveillance Project in Shanghai, China. Two predominant high-risk CRKP clones, ST11-wzi64 and ST15-wzi19/wzi24, caused three point-source nosocomial outbreaks in intensive care unit and/or neurosurgery department potentially by respiratory-route, promoting the co-selection and evolution of multidrug-resistant determinants. Multiple quinolone resistance-determining region (QRDR) mutations occurred in isolates of ST15 (S83F, D87A; S80I), ST11 (S83I, D87G; S80I), and ST218 (D87A; S80I). Plasmid-mediated quinolone resistance determinants, qnrS1, aac(6’)-Ib-cr, oqxAB, were detected in 32 (94.1%) isolates alone or in combination, spreading accompanied with β-lactamases (mainly, KPC-2-type carbapenemase and CTX-M-type extended-spectrum β-lactamase), 16S rRNA methylases (ArmA and RmtB), and putrescine ABC transporter permease (PotI) variants, independently of QRDR-mutations. AcrR, AcrAB transcriptional repressor, was insertion-inactivated by IS5-transposase in isolates of ST11. Thirteen ompK36 variants associated with specific ST (n=7) and wzi-allele (n=9) clustered into 10 (sub)lineages in the phylogenetic tree possibly affecting the MDR phenotype and the infection outcome of isolates. Isolates of ST11, ST15, and ST218 had frameshift disruptions in OmpK35 coupled with specific GD-insertion at position 134-135 in OmpK36, all showing distinct microevolution clusters of ompK36 genotypes. Seven quinolone-susceptible isolates kept the porin genes integral, including two each CRKPs of ST13-wzi74 (carbapenemase KPC-2 and NDM-1-coproducers) and ST65-wzi72.
Conclusions
Under selective pressures, accumulation of mutations of three types (QRDR, AcrR, OmpK36/OmpK35) and acquisition of resistance-conferring genes has been continuously contributing to quinolone-resistance in clinical MDR-KP isolates, reinforcing the importance of ongoing epidemiologic surveillance on the evolution and transmission of these isolates. Our findings provided detailed mechanistic analyses and epidemiologic implications for further infection control and antibiotic stewardship initiatives.