Vaccination of turkeys with cell-free culture filtrate of Pasteurella multocida: effects of ultrafiltration and endotoxin removal.

Cell-free culture filtrate (CCF) of Pasteurella multocida strain R44/6 (serotype 3/4/9/12) was fractionated by ultrafiltration into fractions of less than 10,000, greater than 10,000, greater than 30,000, and 10,000 to 30,000 molecular weight (MW). The less-than-10,000-MW fraction contained little endotoxin comparable to bacteriologic medium; the 10,000-to-30,000-MW fraction had a moderate amount of endotoxin, whereas the greater-than-10,000- and greater-than-30,000-MW fractions contained high levels of endotoxin. Following ultrafiltration, each fraction, except the less-than-10,000-MW fraction, was divided into two equal parts, and endotoxin was removed from one part. Turkeys were vaccinated with the various MW fractions of CCF, with and without endotoxin, via the air sacs at 6 and 9 weeks of age and compared with negative controls given bacteriologic medium and positive controls vaccinated with a commercial bacterin. Before oral challenge with strain P-1059 (serotype 3) at 12 weeks of age, antibody titers were detected only in positive control turkeys. Protection against challenge, as measured by post-challenge mortality and body-weight gain, was provided by the greater-than-10,000-, greater-than-30,000-, and 10,000-to-30,000-MW fractions containing endotoxin and the commercial bacterin. Turkeys that had been vaccinated with bacteriologic medium and the four different fractions without endotoxin were not protected. Results indicated that endotoxin in CCF of P. multocida is critical in protecting turkeys from pasteurellosis.