Lysates of turkey-grown Pasteurella multocida: examination of vaccine preparations by electron microscopy.

The effects of differential centrifugation, density gradient centrifugation, freeze-thawing, and chemical lysis on the morphology of Pasteurella multocida from the blood of infected turkeys were examined by electron microscopy. Morphologic differences were not seen between thin-section preparations of P multocida after differential and density gradient centrifugation procedures. The internal ultrastructure of in vivo-grown cells was different from that observed previously for P multocida grown in vitro. Large membranous blebs were also observed on the surface of negative-stained preparations of organisms from the plasma, but not in thin sections of cells from the same preparation. Freeze-thaw of bacterial suspensions in sucrose resulted in partial lysis, revealing bacteria in different phases of degradation. Complete lysis (but not solubilization) was enhanced by treatment with EDTA, lysozyme, and Triton X-100. Centrifuged lysate pellets were thin-sectioned or negative-stained. Pellets consisted of vesicles, ranging in size from 0.05 to 1.0 micrometer, that had a characteristic trilaminar membranous appearance similar to those reported from other gram-negative bacteria grown in vitro and treated similarly.