THE ROLE OF CAPSULAR MATERIAL OF PASTEURELLA HAEMOLYTICA, TYPE 1, IN BOVINE PNEUMONIC PASTEURELLOSIS (CYTOTOXIN)

Scope and Method of Study. This study was undertaken to examine the relationship of capsular material on Pasteurella haemolytica to the organism itself and to the organism's role in bovine pneumonic pasteurellosis. It was necessary first to develop a staining technique whereby encapsulation of the organisms could be determined rapidly and a capsular extraction method which would remove capsular material with minimal resultant decrease in culture viability. Capsular extraction was then used to prepare comparable populations of encapsulated and decapsulated organisms and solutions of extracted capsular material. The interactions of encapsulated and decapsulated organisms with bovine sera and with bovine phagocytes were compared, and the capsular extract was characterized and compared to three different preparations of P. haemolytica cytotoxin.;Extracted capsular material contained protein and carbohydrate and was immunogenic. It was shown not to be related immunologically or toxicologically to P. haemolytica cytotoxin. A study of cytotoxin neutralization by bovine sera revealed that significant cytotoxin neutralizing capacity depended on exposure of cattle to live, metabolically active organisms. Cytotoxin neutralizing capacity was an important determinant of the animal's resistance to experimental disease.;Findings and Conclusions. Capsules were demonstrated on organisms from logarithmic-phase cultures of P. haemolytica. The amount of capsular material on the bacteria diminished as cultures aged, until little capsular material was demonstrable on organisms from stationary-phase cultures. Decapsulation of the organisms, which was accomplished at 41(DEGREES)C for 1 hr, resulted in loss of an antigenic component and in an increased sensitivity to antibody-mediated agglutination. Decapsulated bacteria were also more sensitive than were encapsulated ones to the bactericidal action of several bovine sera. Neither encapsulated nor decapsulated bacteria were phagocytized by bovine phagocytes in the absence of specific antibody, whereas both types of organisms were phagocytized after opsonization with antisera. Encapsulation did not appear to enhance resistance to phagocytosis. Both encapsulated and decapsulated organisms were toxic for bovine phagocytes. Intracellular killing of organisms was demonstrated by transmission electron microscopy but could not be determined by a viable-counting technique.