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

Hypermucoviscosity (hmv) is a capsule-associated phenotype usually linked with hypervirulent strains. The key components of this phenotype are the RmpADC proteins contained in non-transmissible plasmids identified and studied in . is closely related to and recently has been identified as an emergent human pathogen. a normally contains plasmids, some of them carrying antibiotic resistance and virulence genes. Previously, we described a clinical isolate showing an hmv-like phenotype that harbors a 343-kb pKV8917 plasmid. Here, we investigated whether pKV8917 plasmid carried by 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 ( < 0.001) and virulence. In addition, pKV8917 was successfully transferred to and strains via conjugation. Notably, when pKV8917 was transferred to , the transconjugants displayed an hmv-like phenotype, and capsule production and virulence increased; these phenotypes were not observed in the 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 / 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 and multidrug-resistant . The pKV8917-unique region harbors a cellulose biosynthesis cluster (), fructose- and sucrose-specific () phosphotransferase systems, and the transcriptional regulators and , respectively, involved in membrane permeability. The hmv-like phenotype has been identified more frequently, and recent evidence supports the existence of /-independent hmv-like pathways in this bacterial genus.