| Rhodococcus equi is a facultative intracellular respiratory pathogen of foals that persists and multiplies within macrophages. Virulence is associated with 80-90 kb plasmids, which include a pathogenicity island (PI) containing the vap (virulence-associated protein) gene family. However, the role of chromosomal genes in virulence is not known. Preliminary analysis of a partial (25-30% coverage) genome sequence of R. equi described in this thesis revealed homologues of Mycobacterium tuberculosis putative virulence genes. A mini-DNA microarray was developed with 43 selected putative R. equi chromosomal virulence genes and eight PI genes to study their transcription during growth of R. equi in vitro (37° C, pH 5.0), under oxidative stress conditions (50 mM H2O2, 30 minutes) and inside equine peripheral blood macrophages. choD, clpB, fadD13, fbpB, groEL, hemE, mbtF, moxR, and sigK were chromosomal genes significantly transcribed in R. equi inside macrophages. The expression pattern of R. equi chromosomal genes transcribed significantly inside macrophages differed from those transcribed under in vitro conditions. |
