A COMPARATIVE-STUDY OF BOVINE AND OVINE HAEMOPHILUS-SOMNUS ISOLATES

Bacterial isolates (including 17 Haemophilus somnus isolates and an H. somnus-like isolate) from asymptomatic or diseased cattle and sheep, were evaluated for markers associated with virulence and host predilec tion, The isolates were separated into 6 distinct biovariants, 3 for s heep and 3 for cattle, based on reactions in a battery of 21 test medi a, Three bovine isolates associated with disease caused hemolysis of b ovine blood, The rest of the isolates did not hemolyze either bovine o r ovine erythrocytes, Protein profiles of all H, somnus isolates were similar with the exception of the major outer membrane proteins (MOMPs ), The MOMPs of isolates associated with disease in cattle had a relat ive molecular weight of approximately 41 kDa compared with 33 kDa for the MOMPs of isolates from asymptomatic cattle, The MOMPs from sheep i solates were either slightly higher or lower than the 41 kDa MOMPs of bovine isolates, Major antigens detected by Western blotting were simi lar in all isolates except the H, somnus-like isolate, An immunodomina nt 40 kDa antigen was conserved in all H, somnus isolates, Antibodies to this antigen have previously been found to be protective in cattle and may also be protective for sheep, Marked differences between cattl e and sheep isolates were revealed by use of restriction enzyme analys is, which separated the isolates into 12 ribotypes and 15 unique DNA p rofiles. Thus, cattle and sheep isolates in this collection had distin ctive differences in biochemical reactions, MOMP profiles, and DNA ana lyses, Such differences have potential value for epidemiological studi es and may also be used to evaluate host specificity of H. somnus isol ates.