Molecular characterization of virulence-associated protein (Vap) family genes of pathogenic Rhodococcus equi isolates from clinical cases of Indian equines.

Abstract

Virulence-associated plasmid (Vap) genes of clinical isolates of Rhodococcus equi were characterized. Isolates were identified by 16S rRNA, choE and traA gene PCR, followed by amplification, cloning and sequencing of 7 Vap genes. The isolates were found positive for vapA gene family. The comparative sequence analysis of vap genes revealed 99-100% similarity at both nt and aa levels with all sequences. The aa sequences of the predicted Vap proteins exhibited a high degree of similarity to each other, especially at the carboxy terminal ends. Invariable point mutations were observed in Vap proteins. The changes did not cause alteration in hydropathicity and secondary structures in VapA & H proteins. Few major changes in polarity and structures were observed in VapD, E and G proteins. Phylogenetic analysis revealed that all Vap genes followed similar branching pattern except isolate from Bahadurgarh (BBG163). We conclude that VapA is highly conserved and plays a major role in pathogenesis. This is the first report of sequence analysis and phylogenetic studies of Vap gene family of clinical virulent isolates of R. equi from India