Evolution of Virulence, Fitness, and Carbapenem Resistance Transmission in ST23 Hypervirulent Klebsiella Pneumoniae with the Capsular Polysaccharide Synthesis Gene Inserted Via Insertion Sequence Elements

Carbapenem-resistant hypervirulent Klebsiella pneumoniae (CR-hvKP) is recognized as a threat worldwide, but the mechanisms underlying its emergence remain unclear. As most CR-hvKP isolates are not hypermucoviscous, we speculated that the evolution of the capsule might result in the convergence of carbapenem resistance and hypervirulence. Here, 2,096 K. pneumoniae isolates were retrospectively collected to screen the ST23-K1 clone, and hypervirulence was roughly defined as being highly resistant to serum killing. The effect of on the capsule, virulence, fitness, and resistance acquisition was further analyzed. The capsule gene , inserted by IS/IS, was identified via whole-genome sequencing in four hvKP, but not hypermucoviscous, isolates. Uronic acid quantitation results revealed that these isolates produced significantly less capsular polysaccharides than NTUH-K2044. A significant increase in capsular production was observed in -complemented isolates and confirmed by transmission electron microscopy. Further, all -complemented isolates acquired greater resistance to macrophage phagocytosis, and one representative isolate resulted in a significantly higher mortality rate than the parental isolate in mice, indicating that inactivation might compromise virulence. However, isolates with interruption demonstrated a lower fitness cost and a high conjugation frequency of the plasmid, raising concerns about the emergence of carbapenem resistance in hvKP. Klebsiella pneumoniae is one of the most common nosocomial pathogens worldwide, and we speculated that the evolution of the capsule might result in the convergence of carbapenem resistance and hypervirulence of K. pneumoniae. The gene was first reported to be interrupted by insertion sequence elements in ST23-K1 hypervirulent Klebsiella pneumoniae, resulting in little capsule synthesis, which plays an important role in virulence. We examined the effect of on the capsule, virulence, and fitness. Isolates with interruption might compromise virulence and demonstrated a lower fitness cost and a high conjugation frequency of the plasmid, highlighting its role as a potential factor facilitating hypervirulence and carbapenem resistance.