Ultrastructural observation of nasal and pulmonary intracellular Pasteurella multocida A : 3 in rabbits

Sixteen 8- to 9-week-old Pasteurella multocida-free rabbits were divided in to two equal groups. Eight rabbits in one group were inoculated intranasall y with P. multocida type A:3. The other eight were inoculated intranasally with phosphate-buffered saline and used as controls. Nasal swabs taken befo re and after inoculation were cultured for bacterial isolation. Post-mortem nasal swabs and lung samples were cultured for bacteriological isolation. Nasal mucosa and lung samples were collected and processed for transmission electron microscopy. Pasteurella multocida was isolated from the nasal cav ity of all infected rabbits and from the lungs of four infected rabbits. De generative ultrastructural changes in epithelial cells and endothelial cell s were seen in the infected rabbits. Deciliation of the cilated epithelium and hyperplasia of the goblet cells in the nasal mucosa were noted. Thicken ing of the alveolar septa due to hyperplasia of type II pneumocytes, swelli ng of the endothelial lining of capillaries and infiltration of inflammator y cells were also observed. Intracellular invasion of the nasal epithelial cells and of type II pneumocytes by the organism was observed. Coccobacilli were observed in membrane-bound vacuoles in the cytoplasm of these cells. The vacuoles were adjacent to the host-cell mitochondria and some of these vacuoles appeared to be fused to the mitochondrial membrane. Some type I pn eumocytes with intracellular membrane-bound vacuoles containing bacterial c ells showed protrusions, which appeared to detach into the alveolar lumina. These results indicated that P. multocida serotype A:3 in rabbits can inva de the epithelial cell and cause structural changes in the interstitium, ep ithelium and endothelium. Heterophils and macrophages appear to play import ant roles in tissue injury.