الفهرس 
INTRODUCTION
The Aim of the WorkOnly 14 pages are availabe for public view
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Abstract
P. multocida isolate used in the present study was obtained from the Animal health Research Insititute,Dokki, Cairo. The Pasteurella multocida strain used for experimental infection was isolated from a fatal case of acute fibrinous pneumonia in a domestic rabbit obtained from a commercial rabbitry which had an enzootic of pasteurellosis characterized by acute fibrinous pneumonia, and was identified according to (OIE,2008). The strain produced fatal systemic pasteurellosis following intraperitoneal inoculation of adult mice. The isolated strain was grown on trypticase soy agar and dextrose starch agar in Roux flasks for 24 hours at 37˚C. Bacteria were collected by flooding the agar surface with phosphate buffered saline (PBS) and adding glass beads. The number of colony-forming units (CFU) in the stock inoculum was determined by standard plate counting techniques. Serial dilution of the stock inoculum using phosphate buffered saline (PBS) to be adjusted to 106cfu/ml was used in intranasal infection in the experimental rabbits.
In the present experiment, eighteen rabbits (8- 9 weeks-old) will be purchased from Assiut laboratory house (Assiut University) The rabbits were housed individually in stainless-steel cages in separate animal care facilities and provided with water and rabbit pellets ad libitum. Bacterial isolates were pelted, fixed in 4% gultraldehyde and critical point drying and examined by scanning electron microscope. Bacterial isolates were pelted, fixed in 4% gultraldehyde and critical point drying and examined by scanning electron microscope. Eighteen rabbits which were free from P. multocida, were divided into two groups.
Group A (sixteen rabbits) were inoculated intra-nasally with 106/ml cell of bacteria isolated from field cases in 1 ml of PBS by inserting a syringe without needle and gently expressing the inoculums to avoid any injury to the nasal mucosa.
Group B (two) Two rabbits of this group will be inoculated with 1ml PBS and used as a control group. Samples from the nasal mucosa (both sides), middle part of trachea and from all the lobes of the lungs, and hearts, of all rabbits from both exposed and control groups were taken and fixed in 10% neutral buffered formalin , processed , and stained by H&E for light microscopical examination.
Pasteurella mulocida appeared as pleomorhic cocco-rod to bipolar shaped in blood films stained by Giemsa stain. Aggregation of bioplar-rod shaped bacteria with capsule by scanning electron microscope. Moreover, broad capsule was identified for single isolates. There were no fimbriae or pilli observed at the level of Scanning EM.
The thoracic cavity showed various degrees of congestion of the lungs, trachea, and hearts. Various degrees of lung hemorrhage and paleness of the lungs compared to the control were also observed. The main microscopic changes were observed in the nasal mucosa, trachea, lungs, and heart during the duration of the experiment. The nasal cavity of rabbits in the present study was the site of inoculation.
Histologically, the nasal cavity is consisted of nasal mucosa, submucosa, mucus glands, and cartilage. The main microscopic changes were observed mainly during the first 3-4 days post-inoculation. Few inflammatory cells in the submucosa by the second day post-inoculation as well as focal aggregation of lymphocytes were also observed in this time interval. Erosion of the nasal mucosa and hypertrophy of mucus glands were noticed by the 4th day post-inoculation.
The tracheal changes were prominent and manifested by hyperplasia and hypertrophy of mucus cells, disorganization of cilia and slight hyperemia of sub-mucosal blood vessel. Prominent lymphocytic inflammatory cellular reaction was evident in the submucosa by the 5th day post-inoculation. Hyperemia of the submucosal blood vessels was observed at the 6th and 7th day post-inoculation. The lungs in the present study showed features of pneumonia. These changes were expressed by infiltration of macrophages and lymphocytes in the alveoli as well as thichening on the alveolar septa. There was grading of inflammatory cells during infection.
The ultrastructural changes of the nasal mucosa examined by SEM in the present study showed desquamation of the nasal epithelium by the 7th days post-inoculation and became more obvious by the 14th days. These results could be attributed to the presence and adherence of the inoculated bacteria.
In conclusion, P. multocida used in this study by SEM did not show any evidence for pilli , only broad capsule and could be attributed to its main pathogenic virulence mechanism. The main organs affected are the nasal cavity, trachea, lungs and heart. Other organs examined are considered non-specific to Pasteurella. The morphological changes observed in this study were coinciding with clinical signs noticed during the exposure period. Pneumonia and grading of inflammatory cells were evident. Desquamation of nasal cavity and attachment of bacteria are observed even at 14 days post-inoculation by SEM and suggesting rhinitis.