VIRULENCE REGIONS AND VIRULENCE FACTORS OF THE OVINE FOOTROT PATHOGEN, DICHELOBACTER-NODOSUS

Ovine footrot is a debilitating and highly infectious disease that is primarily caused by the Gram-negative, anaerobic bacterium Dichelobact er nodosus. The major antigens implicated in virulence are the type IV fimbriae and extracellular proteases. The fimbriae show sequence and structural similarity to other type IV fimbriae, this similarity exten ds to genes that are involved in fimbrial biogenesis. Several acidic a nd basic extracellular serine proteases are produced by both virulent and benign isolates of D. nodosus. Subtle functional differences in th ese proteases appear to be important in virulence. In addition, there are two chromosomal regions that have a genotypic association with vir ulence. The partially duplicated and rearranged vap regions appear to have arisen from the insertion of a plasmid into a tRNA gene via an in tegrase-mediated site-specific insertion event. The 27 kb mi region ha s several genes often found on bacteriophages and has inserted into an ssr A gene that may have a regulatory role in the cell. The determina tion of the precise role that each of these genes and gene regions has in virulence awaits the development of methods for the genetic analys is and manipulation of D. nodosus.