The Influence of Carbohydrates on the Virulence Potential of <i>Klebsiella variicola</i> Isolates

<i>Klebsiella variicola</i> is a Gram-negative bacillus belonging to Enterobacteriaceae recognized as an emerging human pathogen in the last years. The species is frequently misidentified as <i>Klebsiella pneumoniae</i> by conventional microbiological tests, raising questions about its real prevalence and clinical impact. <i>K. variicola</i> virulence is mediated by traits that are expressed in human body niches containing different nutrients, including carbohydrates, that influence their expression. In this way, we analyzed the effect of different carbohydrates on the expression of virulence traits by <i>K. variicola</i> isolates. For this approach, three classical strains (cKv15, cKv35, and cKv57) and one hypermucoviscous (HMV) were submitted to growth curve characterization, biofilm production and serum survival assays, siderophores, and <i>mrk</i>A (encoding MRK adhesin) RNA quantification. The strains were cultivated in broth containing specific carbohydrates as the sole carbon source to perform the assays. Among all carbohydrates tested, sorbitol, galactose, and maltose were the most effective in promoting biomass production in biofilm for the <i>K. variicola</i> classical strains (cKv). Additionally, bacterial incubation in these carbohydrates resulted in the production of siderophores by all strains (cKv and HMV). Notably, cKvs cultivated in all carbohydrates tested survived and proliferated in human serum, while also producing high concentrations of siderophores and biofilm biomass. Except for siderophore production, HMV did not present any virulence trait tested (biofilm production, serum survival, and <i>mrk</i>A expression). However, its growth in media supplemented with galactose promoted serum survival. These observations indicate cKv isolates were able to use sorbitol, galactose, and maltose for rapid proliferation and to express determinants associated with bacterial colonization (as biofilm production, siderophores, and serum survival). The hypermucoviscosity of HMV did not promote biofilm and siderophore production. For this strain, galactose promoted survival in human serum. Altogether, the results highlight the role of galactose in promoting virulence in <i>K. variicola.</i>