Effect in virulence of switching conserved homologous capsular polysaccharide genes from Klebsiella pneumoniae serotype K1 into K20.

The capsular polysaccharides in different serotypes ofKlebsiella pneumoniae(KP) coded by the (CPS) gene cluster are characterized by a conserved and a hyper-variable region. We performed a virulence study by switching genes in the highly conserved region of the CPS cluster between strains. Six genes in the CPS conserved region in serotype K20, includinggalF, acidPPc, wzi, wza, wzbandwzc, were knocked out and replaced by the homologous genes from serotype K1. Compared to the parental K20 strain, the mutants showed a decline in lethality (LD50) in mice from 10-fold to > 105-fold and were categorized in terms of the effect on virulence as low (L) forgalFandacidPPC, moderate (M) forwzi, and high (H) forwza, wzbandwzc. Although substituting theacidPPCgene from K1 foracidPPCin the K20 strain fully restored virulence, substitution with thewzi, wza, wzborwzchomologs from K1 did not. The restoration withwzifrom K1 led to a partial restoration of virulence, with the LD50in mice changing from 104to 103CFU.For thewza, wzbandwzcgenes, Complementation of K20wza, wzbandwzcfrom K1 resulted in varied degrees of lethality in mice. Variable improvement in serum killing and phagocytosis was observed when the knockout mutants were compared with the gene-switched strains. In conclusion, homologous genes for capsule synthesis failed to exhibit the same functionality when switched between serotypes and virulence was decreased in different degree in according to the genes' homology. [ABSTRACT FROM AUTHOR]