PARTIAL CHARACTERIZATION OF THE LEUKOTOXIN OF PASTEURELLA HAEMOLYTICA-LIKE BACTERIA ISOLATED FROM SWINE ENTERITIS

Pasteurella haemolytica-like (PHL) strains isolated from diarrheic pig s are known to produce a leukotoxin that is lethal to ruminant leukocy tes. In the present study, 12 PHL strains were screened for leukotoxin production using a tetrazolium dye-reduction assay. Sterile culture s upernatant from strain 6213A, the maximum leukotoxin producer, was use d as the crude leukotoxin for characterization studies. The leukotoxin was inactivated by heat at 60 degrees C and by trypsin, protease, and amylase. Toxicity was retained over a pH range of 3.0-11.0. The leuko toxin was lethal to polymorphoneutrophils (PMNs) of cattle, sheep, goa t, and swine. Chromosomal DNA of all 12 PHL strains hybridized with a 3.9 kb Pasteurella haemolytica A1 leukotoxin probe, indicating similar ities between the leukotoxin genes of P. haemolytica and PHL strains.