Identification of Klebsiella pneumoniae genes uniquely expressed in a strain virulent using a murine model of bacterial pneumonia

Klebsiella pneumoniae is a gram-negative bacterium of significant clinical importance. This study examines the differential pulmonary host anti-bacterial responses towards two clinical isolates of K. pneumoniae. Intratracheal inoculation with 7×104 CFU of strain 43816 induced 100% mortality in C57BL/6J mice within 5 days post infection, whereas infection with 5×105 CFU of strain IA565 resulted in 100% survival. Infection with strain 43816 resulted in significant pulmonary and peripheral blood bacterial burden and induction of the chemokines MIP-2, KC and MCP-1 by 24 h post infection. In contrast, IA565-infected mice displayed basal chemokine levels and no detectable bacteria by 24 h post inoculation were isolated from lungs or peripheral blood. These data indicate an apparent lack of pathogenicity of strain IA565. Since little is known about Klebsiella-specific virulence genes, we have utilized PCR-based genomic DNA and cDNA suppressive subtractive hybridization and identified nine DNA sequences unique to the pathogenic strain of K. pneumoniae 43816. These sequences were highly homologous to enteric bacterial genes regulating iron uptake, fimbrial-mediated adhesion, energy production and conversion, transcriptional regulation, signal transduction, restriction endonuclease activity, and membrane transport.