Ultrastructural pathology Associated with Attachment of Pasteurella multocida serotype B: 2 to Tracheal and Pulmonary Endothelial Cells and Tracheal cilia of Mice

Mice infected intraperitoneally with P. multocida at the dose of 10 7 cells showed trachea with loss of cilia. The cilia become deformed with electron dense outline and bacterial cells were seen attached to the deformed cilia. Many bacteria were also seen closely attached to endothelial cells causing several ultrastructural changes at the sites of attachment. The cytoplasm at the site of bacterial attachment appeared to extend into either short or long pedestal (attaching and effacing lesions) into the blood vessel lumen with a single bacteria attached to the pedestal. These pedestals are either electron dense or electron dense and vesicular. Occasionally, beneath these cytoplasmic extensions, focal increased in electron density of the cytoplasm were observed. Also, there were long thin, single cytoplasmic extensions (microvillus-like protrusions) around the attached bacteria. Invagination with two fingers like cytoplasmic extensions which appears to engulf the attaching bacteria were also seen. The cell membrane of some endothelial cell adjacent to the attached bacteria appeared depressed / invaginated.