Purpose: In clinical settings, CG23 Klebsiella pneumoniae (Kp) is the most virulent clonal group of Kp. Continuous fusions of hypervirulent (Hv) and highly resistant strains have been reported; however, few studies have analysed the molecular epidemiology and clinical characteristics of CG23 strains, especially MDR-sequence type ST23 strains. In this study, we investigated the molecular characteristics of ST23 Kp and analysed the clinical characteristics of ST23 Kp infections in a large teaching hospital of the third class in China.
Methods: ST23 Kp isolates were screened using whole-genome sequencing data from a large single centre. We compared the clinical characteristics of ST23 strains isolated from community-acquired infections (CAI) and hospital acquired infection (HAI). In addition, the infection characteristics of MDR and poor-prognosis isolates were investigated. We analysed genetic characteristics of ST23 Kp and further investigated the evolutionary relationship based on single-nucleotide polymorphism phylogenetic trees.
Results: We detected 184 ST23 strains between 2013 and July of 2018. There were no significant differences between the isolation rates of pulmonary, bloodstream, urinary tract, and cutaneous soft tissue infections in the community and hospitals, except for abscess infections. MDR strains primarily cause pulmonary infections and abscesses; infections with a poor prognosis are typically bloodstream and pulmonary infections. Fourteen MDR strains producing extended-spectrum or class C beta-lactamases, resulting in resistance to third-generation cephalosporins. In 3.8% of ST23 Kp strains, the clb locus was absent. The phylogenetic tree revealed that the isolates were primarily divided into three clades, and based on clinical data, it is inferred that three clonal transmission events have occurred, mainly in ICU causing lung infection.
Conclusion: This study demonstrates that virulence and drug-resistance fusion events of ST23 strains occur gradually, and that the hypervirulent clones facilitate the widespread dissemination of CAI and HAI, particularly pulmonary. Monitoring genomics and developing antivirulence strategies are essential.

Keywords: Klebsiella pneumoniae, ST23, multidrug-resistant, community-acquired infection, nosocomial infection, pneumonia