Geneticand phenotypic characterization of a novel ST45-K43 carbapenem-resistant <i>Klebsiella pneumoniae</i> strain causing bloodstream infection: a potential clinical threat

<i>Klebsiella pneumoniae</i> is a common pathogen of nosocomial infection, which can cause pneumonia, urinary tract infection, cystitis, and bloodstream infections (BSIs). Here, we genetically characterize a novel carbapenem-resistant <i>K. pneumoniae</i> (CRKP) strain recovered from the blood of a 44-year-old male patient with severe acute necrotizing pancreatitis and septic shock in China. The strain is a ST45 <i>K. pneumoniae</i> with a novel serotype of K43, named 18SHX166. The susceptibility testing results showed that 18SHX166 was resistant to cephalosporin and carbapenems but still susceptible to ceftazidime-avibactam, quinolones, colistin, and amikacin. Genomic sequencing revealed that 18SHX166 contains three plasmids, namely pSHX166-Hv, pSHX166-KPC, and pSHX166-3. pSHX166-Hv harbored the <i>iucABCD</i> operon, encoding the siderophore of aerobactin. pSHX166-KPC harbored <i>bla</i>_KPC-2 gene and possessed complete conjugative regions. The conjugation experiment verified pSHX166-KPC as a self-transmissible plasmid mediating the dissemination of antibiotic resistance, with a conjugation rate of 2.21 × 10^-5. Additionally, the growth curve showed that 18SHX166 demonstrates a higher growth rate than the control strains. The characteristics of 18SHX166 indicate a potential high risk of clinical transmission.IMPORTANCEST45-K43 carbapenem-resistant <i>Klebsiella pneumoniae</i> isolate, 18SHX166, carries a carbapenem resistance plasmid and virulence plasmid. It has the characteristics of multidrug resistance, high transmissibility, and a fast growth rate, which could pose a threat to the control of antimicrobial resistance and clinical transmission, causing a severe challenge to public health.