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Gene Review

vapA  -  virulence associated protein VapA

Rhodococcus equi

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Disease relevance of vapA


High impact information on vapA

  • Complementation analysis of the vap locus mutant showed that expression of vapA alone could restore full virulence, whereas expression of vapC, -D and -E could not [2].
  • Deletion of vapA encoding Virulence Associated Protein A attenuates the intracellular actinomycete Rhodococcus equi [2].
  • These studies provide the first proof of a role for vapA in the virulence of R. equi, and demonstrate that its presence is essential for intracellular growth in macrophages [2].
  • Since our results showed that vapA, vapD, and vapG are genes highly induced by macrophage-related stresses, their gene products may, within the Vap protein family, play a dominant role inside these phagocytic cells and may be the most promising candidates for vaccination strategies [3].
  • The transcriptional start site of vapA was determined to be a cytidine located 226 bp upstream from the vapA initiation codon [1].

Biological context of vapA

  • The most striking feature of the virulence plasmids was the presence of a 27,536-bp pathogenicity island containing seven virulence-associated protein (vap) genes, including vapA [4].
  • Moreover, we identify three additional genes carried on the virulence plasmid, vapC, -D, and -E, that are tandemly arranged downstream of vapA [5].
  • Radiolabelled PCR product derived from the R. equi rrnA gene and specific hybridization conditions enabled differentiation of colonies of R. equi from environmental species, whilst radiolabelled PCR product derived from the R. equi vapA gene, under specific hybridization conditions, allowed differentiation between avirulent and virulent R. equi [6].
  • 0. One operon, containing vapA, was monocistronic whereas the other was polycistronic composed of vapD and an unknown open reading frame [7].
  • A putative consensus IdeR binding site was identified upstream of vapA, suggesting that vapA is a member of an IdeR regulon in R. equi [8].

Anatomical context of vapA

  • We developed a DNA vaccine expressing the vapA gene (pVR1055vapA) that induced an anamnestic response characterized by virulence associated protein A (VapA)-specific IgG antibodies in sera and bronchoalveolar lavage fluid (BALF) as well as VapA-specific proliferation of pulmonary lymphocytes when tested in adult ponies [9].

Associations of vapA with chemical compounds

  • A proteomic approach showed that four polypeptides present in the wild-type strain (85F) are missing in the plasmid-cured strain 85F(P-), and by using a DNA macroarray, we identified two plasmid-encoded vap genes, vapA and vapG, whose expression was highly induced by H(2)O(2) treatment [3].
  • PROCEDURE: The multiplex PCR assay included 3 gene targets: a universal 311-bp bacterial 16S ribosomal RNA amplicon (positive internal control), a 959-bp R equi-specific target in the cholesterol oxidase gene (choE), and a 564-bp amplicon of the vapA gene [10].

Other interactions of vapA

  • Whereas the transcript size of vapA was compatible with a monocistronic mRNA, the transcript of vapG was considerably longer [3].
  • Alignment of this sequence with the leader sequences of vapA and vapD, genes previously shown to be induced by acid, revealed significant homologies [3].

Analytical, diagnostic and therapeutic context of vapA

  • None of the 164 isolates contained the vapA gene, and 44 (26.8%) isolates were positive for the vapB gene, showing a product of the expected 827-bp size in the PCR amplification [11].


  1. The LysR-type transcriptional regulator VirR is required for expression of the virulence gene vapA of Rhodococcus equi ATCC 33701. Russell, D.A., Byrne, G.A., O'Connell, E.P., Boland, C.A., Meijer, W.G. J. Bacteriol. (2004) [Pubmed]
  2. Deletion of vapA encoding Virulence Associated Protein A attenuates the intracellular actinomycete Rhodococcus equi. Jain, S., Bloom, B.R., Hondalus, M.K. Mol. Microbiol. (2003) [Pubmed]
  3. H(2)O(2), which causes macrophage-related stress, triggers induction of expression of virulence-associated plasmid determinants in Rhodococcus equi. Benoit, S., Benachour, A., Taouji, S., Auffray, Y., Hartke, A. Infect. Immun. (2002) [Pubmed]
  4. DNA sequence and comparison of virulence plasmids from Rhodococcus equi ATCC 33701 and 103. Takai, S., Hines, S.A., Sekizaki, T., Nicholson, V.M., Alperin, D.A., Osaki, M., Takamatsu, D., Nakamura, M., Suzuki, K., Ogino, N., Kakuda, T., Dan, H., Prescott, J.F. Infect. Immun. (2000) [Pubmed]
  5. Virulence plasmid of Rhodococcus equi contains inducible gene family encoding secreted proteins. Byrne, B.A., Prescott, J.F., Palmer, G.H., Takai, S., Nicholson, V.M., Alperin, D.C., Hines, S.A. Infect. Immun. (2001) [Pubmed]
  6. Identification and differentiation of avirulent and virulent Rhodococcus equi using selective media and colony blotting DNA hybridization to determine their concentrations in the environment. Muscatello, G., Browning, G.F. Vet. Microbiol. (2004) [Pubmed]
  7. Induction of vap genes encoded by the virulence plasmid of Rhodococcus equi during acid tolerance response. Benoit, S., Benachour, A., Taouji, S., Auffray, Y., Hartke, A. Res. Microbiol. (2001) [Pubmed]
  8. Analysis of virulence plasmid gene expression of intra-macrophage and in vitro grown Rhodococcus equi ATCC 33701. Ren, J., Prescott, J.F. Vet. Microbiol. (2003) [Pubmed]
  9. Analysis of anamnestic immune responses in adult horses and priming in neonates induced by a DNA vaccine expressing the vapA gene of Rhodococcus equi. Lopez, A.M., Hines, M.T., Palmer, G.H., Knowles, D.P., Alperin, D.C., Hines, S.A. Vaccine (2003) [Pubmed]
  10. Evaluation of a multiplex polymerase chain reaction assay for simultaneous detection of Rhodococcus equi and the vapA gene. Halbert, N.D., Reitzel, R.A., Martens, R.J., Cohen, N.D. Am. J. Vet. Res. (2005) [Pubmed]
  11. Characterization of virulence plasmids and serotyping of rhodococcus equi isolates from submaxillary lymph nodes of pigs in Hungary. Makrai, L., Takayama, S., Dénes, B., Hajtós, I., Sasaki, Y., Kakuda, T., Tsubaki, S., Major, A., Fodor, L., Varga, J., Takai, S. J. Clin. Microbiol. (2005) [Pubmed]
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