Hypervirulent Klebsiella pneumoniae (hvKp) can cause severe invasive infections in healthy and immunocompromised individuals. However, there is still lack of a consensus definition of hvKp. In this study, we solely focused on the clinical isolates cultured from subcutaneous drainage of community-acquired liver abscess cases, and an hvKp strain was defined on the basis of co-harboring virulence gene regulator of mucoid phenotype A (rmpA)/rmpA2, iucA, iroB, and peg-344. A total of 47 nonrepetitive hvKp isolates were collected from January 2015 to December 2017 in a tertiary teaching hospital in Shanghai, China. All isolates were susceptible to the commonly used antibiotics. Only one strain (RJ-Kp24) had the positive detection of blaCTX-M-14 and was resistant to ceftazidime, cefotaxime, and cefepime. S1-pulsed-field gel electrophoresis (PFGE) and southern hybridization confirmed the presence of a roughly 90 kb blaCTX-M-14-carrying plasmid and a roughly 240 kb virulence plasmid. Further analysis revealed that ST23 (n = 17) sequence type and K1 (n = 20) and K2 (n = 9) serotypes were dominant in hvKp, while only 31.9% (15/47) and 46.8% (22/47) of hvKp isolates displayed hypermucoviscosity and resistance to serum killing, respectively. For further evaluation of the pathogenicity of hvKp, six representative strains were randomly selected. Three strains, RJ-Kp10, RJ-Kp28, and RJ-Kp31, displayed a remarkable resistance to serum killing and neutrophil phagocytosis. Mouse lethality assay revealed that these strains had the 50% lethal dose (LD50) of 102-103 cell forming unit (CFU), while others had the LD50 of 104-105 CFU. These results demonstrated that strain virulence differed significantly within these defined hvKp. The convergence of multidrug resistance and enhanced virulence in K. pneumoniae has presented a major infection control challenge.
Keywords: ESBLs; community-acquired liver abscess; hypervirulent K. pneumoniae; virulence.