Carbapenem-resistant klebsiella pneumoniae exhibit variability in capsular polysaccharide and capsule associated virulence traits

Background. Novel therapies are urgently needed to treat carbapenem-resistant Klebsiella pneumoniae (CRKp)- mediated infection, which constitute a major health threat in the United States. In order to assess if it is feasible to develop anticapsular antibodies as a potential novel therapy, it is crucial to first systematically characterize capsular polysaccharide (CPS) and virulence traits in these strains. Methods. Forty CR-Kp were genotyped by pulsed field gel electrophoresis, multilocus sequence typing (MLST), and molecular capsule typing (C-patterns and wzi sequencing). Their biofilm formation, serum resistance, macrophage- mediated killing, and virulence in Galleria mellonella were compared. MAb (1C9) was generated by coimmunization with 2 CPSs, and cross-reactivity was investigated. Results. MLST assigned 80% of CR-Kp isolates to the ST258-clone. Molecular capsule typing identified new C-patterns, including C200/wzi-154, which was widely represented and associated with blaKPC-3-bearing strains. Heterogeneity was detected in biofilm formation and macrophage-mediated killing. Differences in serum resistance correlated with virulence in G. mellonella. ST258 strains carrying bla_KPC-3 were less virulent than those with bla_KPC-2. MAb 1C9 cross-reacted with 58% of CR-Kp CPSs. Conclusions. CR-Kp ST258 strains exhibit variability of virulence-associated traits. Differences were associated with the type of KPC gene and CPS. Identification of cross-reacting anti-CPS mAbs encourages their development as adjunctive therapy.