Identification and characterization of the Pasteurella haemolytica leukotoxin

The identification and chromatographic characterization of the leukotoxin of Pasteurella haemolytica is described. The toxin, which has an apparent native molecular weight of greater than 400,000 as judged by gel exclusion chromatography, has a 105-kilodalton (105K) polypeptide as its major protein component. The proteolytic degradation of the 105K polypeptide could be correlated with the loss of toxin activity in aging cultures of P. haemolytica. Antisera raised against purified 105K polypeptide neutralized toxin activity. A 3.9-kilobase-pair fragment of the P. haemolytica genome cloned into a plasmid vector resulted in the production of intracellular toxin in Escherichia coli host cells. The restriction map of this clone shows significant overlap with the map of a previously reported leukotoxin clone (R. Y. C. Lo, P. E. Shewen, C. A. Strathdee, and C. N. Greer, Infect. Immun. 50:667-671, 1985). Finally, antisera raised against the 105K species labeled the P. haemolytica cell surface in a nonuniform, punctate manner.