Toxin production by Pasteurella granulomatis.

Pasteurella granulomatis (Pg) is a recently identified bacterium associated with proliferative fibrogranulomatous panniculitis (also called "lechiguana") in Brazilian cattle. Recent attempts to experimentally reproduce this disease have only been partially successful. We hypothesized that Pg may produce hemolysin(s) and/or cytotoxin(s) which could contribute to its pathogenicity in susceptible cattle. The objective of this study was to determine the presence and degree of hemolytic and leukotoxic activity of selected isolates of Pg. Either ovine or bovine blood agar plates were streaked with 1 of 7 Pg isolates, incubated at 37 degrees C +/- 1 C for 48 hours, and examined for hemolysis. Two of seven isolates showed hemolytic activity on bovine plates, while all seven showed hemolytic activity on ovine plates. By use of the CAMP reaction, involving simultaneous intersecting cultures of Staphylococcus aureus and Pg, all seven Pg isolates showed enhanced (positive CAMP) hemolysis within 24 hours on bovine blood agar plates. Preliminary results using tetrazolium (MTT) dye reductions with bovine neutrophils showed leukotoxicity in 13 of 16 Pg cultures. Alamar blue tests indicate leukotoxic activity for all 7 Pg isolates. We conclude that some Pg isolates have variable hemolytic and/or leukotoxic properties and that this variability (presence and/or degree) of these 2 properties may affect the relative pathogenicity of Pg in susceptible cattle.