Failure of Ribosomes from Nonencapsulated Pasteurella multocida To Protect CF-1 Mice

SUMMARY Monomeric ribosomes (70S) were isolated from nonencapsulated Pasteurella multocida strain X-73 by mechanical disruption and by chemical lysis. Contamination of the initial preparations by lipopolysaccharide (lps) was evident by gel immunodiffusion. Gel filtration chromatography of the 70S ribosomes resulted in ribosomes with lps contamination below the concentration that was detected by gel immunodiffusion, but chickens vaccinated with these preparations responded serologically to lps by producing a detectable titer of passive hemagglutination antibody. Washing the 70S ribosomes through 0.5 M NH4Cl and 30% sucrose rendered them virtually free of contamination by lps as evidenced by lack of passive hemagglutination titer. Ribosomes were evaluated as protective immunogens in CF-1 mice. Two inoculations (14 days apart) at each dosage level of 0.4, 4.0, 40.0, and 400 μg/mouse were given. At 21 days after vaccination, the mice were challenge exposed with encapsulated P multocida X-73 cells. None of the ribosomal preparations (crude or purified) protected against challenge exposure. Killed whole nonencapsulated cells did protect against challenge exposure. In contrast to numerous reports on the effectiveness of ribosomes as protective immunogens, ribosomes from nonencapsulated P multocida cells were not protective immunogens in mice challenge exposed with encapsulated cells under these conditions.