Cytotoxin from an ovine strain of Pasteurella haemolytica: characterisation studies and partial purification

A cell-free, water-soluble cytotoxin from an ovine strain of Pasteurella haemolytica biotype A serotype 1 killed sheep bronchoalveolar macrophages at 37 degrees C, but not at 4 degrees C or 22 degrees C. The cytotoxin was stable over the pH range 2-12, resistant to heat at 60 degrees C but inactivated at 100 degrees C or by autoclaving. Trypsin also destroyed the cytotoxin, which is therefore thought to contain a protein component essential for biological activity. A preliminary purification of the crude cytotoxin using gel-filtration column chromatography resulted in the isolation of a biologically active fraction which resolved as a single protein band and one carbohydrate band on non-dissociating polyacrylamide gels. However, this fraction resolved into approximately 16 component bands on a sodium dodecyl sulphate polyacrylamide gel.