Effect in virulence of switching conserved homologous capsular polysaccharide genes fromKlebsiella pneumoniaeserotype K1 into K20

Abstract

The capsular polysaccharides in different serotypes of Klebsiella 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, including galF, acidPPc, wzi, wza, wzb and wzc, 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 (LD 50 ) in mice from 10-fold to > 10 5 -fold and were categorized in terms of the effect on virulence as low (L) for galF and acidPPC, moderate (M) for wzi, and high (H) for wza, wzb and wzc. Although substituting the acidPPC gene from K1 for acidPPC in the K20 strain fully restored virulence, substitution with the wzi, wza, wzb or wzc homologs from K1 did not. The restoration with wzi from K1 led to a partial restoration of virulence, with the LD 50 in mice changing from 10 4 to 10 3 CFU . For the wza, wzb and wzc genes, Complementation of K20 wza, wzb and wzc from 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 geneswitched 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.

Rhinoscleroma pathogenesis: The type K3 capsule of Klebsiella rhinoscleromatis is a virulence factor not involved in Mikulicz cells formation

“…Conversely, switching the capsule serotype of the K21a strain to virulent K2 resulted in an increased virulence in mouse and in survival in blood and to a lower binding to macrophages [ 38 , 39 ]. In addition, switching highly conserved genes of the capsule cluster involved in capsule export from K1 into K20 hypervirulent strain strongly reduced its bacterial virulence in mice while increasing its neutrophil phagocytosis and survival in macrophages, although it is still not known whether this is due to a change in capsule expression[ 40 ]. However, a recent pan-genomic analysis did not reveal any correlation between capsule serotype and strains responsible of invasive community-acquired infection but rather suggested that the presence of one or several siderophores explains bacterial virulence [ 41 ].…”

Wza gene knockout decreases Acinetobacter baumannii virulence and affects Wzy-dependent capsular polysaccharide synthesis

“…Wza is responsible for transporting capsular polysaccharides from the periplasmic space to the surface of the bacterium, and it participates in the formation of bacterial capsules [21]. Homologues of Wza are found widely in Gram-negative bacteria, and Wza is reported to be a toxic factor in Escherichia coli [22], Klebsiella pneumoniae [23], Riemerella pestis [24], and Vibrio alginolyticus [25]. Other studies have reported the properties of Wza molecules in AB.…”

The contribution of capsule polysaccharide genes to virulence of Klebsiella pneumoniae

“…12 While deletion of galF and acidPPC genes, which are driven by the P1 promoter, 13 had limited effect on virulence, the deletion of genes driven by the P2 promoter (wzi, wza, wzb, and wzc) exhibited moderate to high effects on virulence. The deletion mutants of the latter genes, which are responsible for surface assembly, CPS polymerization, and CPS production, also showed high susceptibility to neutrophilic phagocytosis and to serum.…”

“…In this issue of Virulence, Lin et al 12 describe the contribution of genes located in the highly conserved region of the cps locus to the virulence of K. pneumoniae. In this study, Lin et al identified a serotype K20 strain, which was isolated from a patient with a liver abscess, with high lethality in mice.…”

“…12 However, the study was limited in that it was based on a single strain of each serotype, and thus the relevance of this study's results in regards to other K. pneumoniae strains and serotypes must be explored. In addition, many studies indicate an association between K. pneumoniae serotypes and their severity of infection, 10,14,15 and between production of CPS and antibiotic resistance.…”