Abstract
Klebsiella pneumoniae is a common cause of septicemia and urinary tract infection in immunocompromised patients. In order to identify virulence-associated genes in the bacterium, a PCR-supported genomic subtractive hybridization was employed. Analysis of 30 subtracted DNA clones has revealed 21 distinct nucleotide sequences. Among them, eleven clones were found to be previously identified genes, including those encode the transposase of Tn3926, the capsule polysaccharide synthetic enzymes, an alcohol dehydrogenase and SeqA protein. Three sequences were found to be the homolog of the virulence regulator bvgAS, a two-component signal transduction system of Bordetella pertussis. The rest of the clones, representing 15 distinct sequences, did not exhibit homology with any known genes. Southern blotting analysis using each of these anonymous sequences as a probe has shown that the distribution of these sequences varied greatly in K. pneumoniae clinical isolates, reflecting the heterogeneous nature of K. pneumoniae population. The entire region of the bvg-like genes was subsequently isolated and designated kvg (klebsiella virulence gene). The gene cluster was found to be organized in an unusual structure of kvgASQR, in which KvgS is the sensory histidine kinase, KvgA and KvgR are two highly homologous transcription factors, and KvgQ is likely to be a membrane protein of unknown function. The kvg genes were found to present in approximately 13% of all bacteriemic isolates of K. pneumoniae. By using luxAB as the reporter, we have found that the expression of kvgASQ are activated in the presence of divalent cation chelators, and H2O2. The result suggests that the kvg genes play a role in pathogenesis of K. pneumoniae.Introduction：