Introduction. Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major cause of clinical infection. However, K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae ST15 strains are occasionally identified and have seldom been reported to cause hospital outbreaks in PR China.Hypothesis/Gap Statement. In this study, we describe nosocomial outbreaks caused by KPC-producing K. pneumoniae ST15 strains in a Chinese tertiary hospital.Aim. To characterize the molecular relationship, resistance and virulence factors of the 32 KPC-producing K. pneumoniae ST15 strains isolated in a Chinese hospital.Methodology. A total of 102 non-repetitive carbapenem-resistant Enterobacteriaceae (CRE) strains were collected from a Chinese tertiary hospital in 2018. Multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) were performed to characterize the clonal relationship of the K. pneumoniae isolates, and the ST15 strains were selected for further study. Minimum inhibitory concentrations (MICs) were determined using the broth microdilution method and interpreted according to the Clinical and Laboratory Standards Institute (CLSI) guidelines. Fifteen carbapenem resistance genes, bla _KPC genetic structures and 12 virulence factors were detected by PCR. Whole-genome sequencing (WGS) was performed using next-generation sequencing combined with single-molecule real-time sequencing.Results. Thirty-two K. pneumoniae ST15 strains were characterized, and 31 of them presented a PFGE similarity of >92 %, indicating clonal spread. In 81.3 % (26/32) of strains, the imipenem (IPM) and meropenem (MEM) MICs were ≤8 and≤16 µg ml^-1, while only 1 isolate (KP18069) exhibited ≥64 µg ml^-1 for both agents. The bla _KPC-2 gene embedded in the Tn3-Tn4401 chimaera and synonymous mutations of the ompK35 gene were detected in all the strains. However, a nonsense mutation at amino acid position 248 (K248X) of OmpK36 was found in the highly carbapenem-resistant strain KP18069. No virulence gene was detected in any of the ST15 strains. WGS analyses further confirmed the genetic characteristics of the K. pneumoniae KP18069 strain.Conclusion. Nosocomial outbreaks caused by the clonal spread of K. pneumoniae ST15 strains were characterized in a Chinese tertiary hospital, and strict monitoring of highly resistant CRKP is required.

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