CHARACTERIZATION OF THE LEUKOTOXIN PRODUCED BY DIFFERENT STRAINS OF PASTEURELLA-HAEMOLYTICA

Pasteurella haemolytica isolates from cattle and sheep, including repr esentatives of different serotypes and untypable strains, were examine d for leukotoxin (Lkt) production at the end of the log phase of growt h in brain heart infusion broth. There were marked differences in leuk otoxic activity in culture supernate samples, as measured by chemilumi nescence-inhibition assays with bovine and ovine neutrophils, even bet ween strains of the same serotype. There was also some variation in th e amount and mol.wt of the Lkt protein produced by different strains, as judged by SDS-PAGE, immunoblotting and ELISA. Some strains produced normal amounts of Lkt protein which had only low leukotoxic activity. Most strains produced Lkt of 105 kDa whereas four strains produced a higher mol.wt form of c. 108 kDa, including two of the five serotype A 2 strains examined. Thus, the P. haemolytica isolates showed considera ble heterogeneity in terms of leukotoxin production, mel. wt and activ ity, even within a given serotype.