Transformation of a virulence associated gene of Haemophilus somnus into a strain lacking the gene.

The role of a 76 kDa surface antigen (p76) of Haemophilus somnus in virulence was investigated. The p76 gene from a virulent isolate of H. somnus (strain 2336) was introduced into an asymptomatic carrier strain (129Pt) lacking this gene. This was accomplished by the development of a system for genetic exchange in H. somnus. The cloned p76 gene was inserted into the broad host range vector pLS88, electroporated into H. influenzae for modification and then into the H. somnus strain 129Pt. The recombinant plasmid was characterized from selected transformants and expression of the p76 protein was demonstrated by Western immunoblotting. However, transformants were not serum resistant and surface exposure of the recombinant protein could not be detected, suggesting that additional genetic elements might be required for export.