Wzc mutation enhances virulence in CRKP ST11-KL64 via complement-mediated lysis and lipopolysaccharide release.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) ST11-KL64 has emerged as the dominant subclone in China. Mutations in Wzc confer a hypermucoviscous (HMV) phenotype and enhanced virulence, but how these mutations regulate capsular polysaccharide (CPS) architecture, whether they alter virulence traits, and the mechanisms and consequences of these alterations remain unclear. We found that the WzcY572D mutation in CRKP ST11-KL64 induced HMV phenotype, increased cell-free CPS production, and elongated CPS chain length. In a mouse peritonitis-septicemia model, Wzc mutant strains caused higher lethality, greater cytokine release, more pronounced inflammatory cell infiltration, and severe tissue damage. These mutants also exhibited increased anti-phagocytic ability and greater serum killing activity compared to the non-mutant strain. Elevated lipopolysaccharide (LPS) levels were detected in serum from mice infected with the mutant strains and in normal human serum incubated with these strains. The mutants showed stronger binding to C5b-9 than non-mutation strains. Notably, pretreatment of mice with TAK-242 reduced the lethality induced by CRB113WzcY572D. Collectively, these findings indicate that Wzc mutation in CRKP ST11-KL64 alters CPS spatial distribution and chain length, leading to HMV phenotype acquisition. These changes enhance complement-mediated bacterial lysis. The lysis of bacterial cells results in increased LPS release, and subsequent stronger inflammatory response and more severe tissue damage, ultimately enhances bacterial virulence.IMPORTANCECarbapenem-resistant Klebsiella pneumoniae (CRKP) ST11-KL64 combines multidrug resistance with elevated virulence, posing a significant public health threat. This study demonstrates that Wzc mutation modulates bacteria-host interactions and enhances bacterial pathogenicity through regulating capsular polysaccharide (CPS) architecture. Our findings provide novel insights into the interplay between CPS biosynthesis, the hypermucoviscous phenotype, and virulence in CRKP ST11-KL64.