A Klebsiella variicola Plasmid Confers Hypermucoviscosity-Like Phenotype and Alters Capsule Production and Virulence

Hypermucoviscosity (hmv) is a capsule-associated phenotype usually linked with hypervirulent Klebsiella pneumoniae strains. The key components of this phenotype are the RmpADC proteins contained in non-transmissible plasmids identified and studied in K. pneumoniae . Klebsiella variicola is closely related to K. pneumoniae and recently has been identified as an emergent human pathogen. K. variicol a normally contains plasmids, some of them carrying antibiotic resistance and virulence genes. Previously, we described a K. variicola clinical isolate showing an hmv-like phenotype that harbors a 343-kb pKV8917 plasmid. Here, we investigated whether pKV8917 plasmid carried by K. variicola 8917 is linked with the hmv-like phenotype and its contribution to virulence. We found that curing the 343-kb pKV8917 plasmid caused the loss of hmv, a reduction in capsular polysaccharide ( P < 0.001) and virulence. In addition, pKV8917 was successfully transferred to Escherichia coli and K. variicola strains via conjugation. Notably, when pKV8917 was transferred to K. variicola , the transconjugants displayed an hmv-like phenotype, and capsule production and virulence increased; these phenotypes were not observed in the E. coli transconjugants. These data suggest that the pKV8917 plasmid carries novel hmv and capsule determinants. Whole-plasmid sequencing and analysis revealed that pKV8917 does not contain rmpADC / rmpA2 genes; thus, an alternative mechanism was searched. The 343-kb plasmid contains an IncFIB backbone and shares a region of ∼150 kb with a 99% identity and 49% coverage with a virulence plasmid from hypervirulent K. variicola and multidrug-resistant K. pneumoniae . The pKV8917-unique region harbors a cellulose biosynthesis cluster ( bcs ), fructose- and sucrose-specific ( fru/scr ) phosphotransferase systems, and the transcriptional regulators araC and iclR , respectively, involved in membrane permeability. The hmv-like phenotype has been identified more frequently, and recent evidence supports the existence of rmpADC / rmpA2 -independent hmv-like pathways in this bacterial genus.