الفهرس 
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Abstract
The present study was undertaken to investigate some aspects related to:
1- Epizootiology of different P. multocida outbreak.
2- Isolation and identification of P. multocida isolates morphologically, biochemically and serologically.
3- Whole cell protein profiling.
4- Pathoginicity test on chicken embryos and chickens.
5- Histopathological examination.
6-Evaluation of the efficacy of locally prepared and commercial bacterins.
The present work revealed that P. multocida infections were a great problem in broiler chickens. The epizotiological studies of 120 broiler flocks suspected to suffer from fowl cholera showed that the disease appeared at relatively older age (30-45 day). Morbidity rate ranged from 15% to 30% while mortality rate ranged from 1.0% to 3.5%. P. multocida infections in broilers always take the septicemic form which was always accompanied by leg problems and conjunctivitis. It is suggested to consider fowl cholera in young chickens suffering from arthritis and conjunctivitis.
The present study proved that P. multocida is a gram negative, capsulated, bipolar, non-motile, non-spore forming and facultatively anaerobic bacteria. The isolates were proved to form small non-haemolytic, dew DROP-like non-mucoid and iridescent colonies.
All isolates had a sugar fermentation pattern and biochemical properties similar to the general characteristics of P. multocida. They fermented dextrose, sucrose, mannitol, and galactose, produced variable reaction with xylose, and did not ferment maltose, dulcitol, arabinose, lactose, and salicin. They were catalase and indole positive, but negative for litmus milk, urease, citrate and motility tests. No growth on MaCconkey’s agar and no hemolysis on blood agar.
The current work showed that the culture site of choice from experimentally infected broilers was the tarsal joint followed by the brain. The most pure colonies were obtained from these sites.
All tested isolates taken from broiler chickens belong to the capsular serogroup A. The frequency of Heddleston,s somatic serotypes isolated from broiler chickens in the present results was the highest for serotypes 1, 3.4 (42.9% for each) followed by serotype 3 (14.3%). This serotyping distribution is comparable to the findings of others. It may be concluded that the frequency of the somatic serotypes of the isolates depends upon the age and species from which these isolates are taken.
In the whole cell protein profile most of isolates were similar specially at molecular weights 84, 58, 39, 35 and 20, which are representing the major proteins on the bacterial surface, the matter which reflect the complete homology among the different tested isolates. Serotyping results showed that all isolates belong to capsular serotype A, this order confirms the results of the whole cell protein profile specially the surface soluble proteins.
The embryonating chicken eggs are suitable laboratory hosts for studying the difference in pathogenicity among different strains of P. multocida. All isolates killed chicken embryos but after variable time. Serotypes 1 and 3 killed chicken embryos 24 hours postinoculation and caused severe septicemia, while serotype 3.4 killed them 48-72 hours postinoculation and the septicemic picture was less severe. Histopathologically, the P. multocida was demonstrated intracellularly in the hepatocytes of the infected chicken embryos.
In pathogenicity test, chickens were experimentally infected by three routes: oral, intra ocular and intramuscular. The intramuscular route caused the most quickest onset as well as the highest morbidity. Mortalities (20%) were seen only in birds infected through the intramuscular route. It can be postulated that the virulence of P. multocida is affected by the route of inoculation.
The twice vaccination with prepared bacterins induced good immunity (80-90%) against challenge with the P. multocida of homologous immunogeneic type. 80% protection rate was obtained against homologous challenge with serotype 3.4 and 90% against homologous challenge with serotypes 1 and 3. However, the bacterins induced a relatively low protection (10-30%) against heterologous challenge. Serotypes 3.4 and 3 bacterins induced a relatively high protection compared with serotype 1 bacterin.
The current study indicated that the prepared polyvalent bacterin induced a good immunity (80-90% protection) against challenge with the three serotypes 1, 3.4 and 3. on the other hand The commercial vaccine, induced a moderate protection rate of 40, 50 and 60% against challenge with serotypes 1, 3.4 and 3 respectively. In conclusion, locally prepared polyvalent bacterins should be used in cases of fowl cholera outbreaks.
Although all isolates in the present study belong to the capsular serogroup A, the prepared bacterins afforded relatively low protection (10-30%) against the hetrologous challenge. It can be postulated that the capsular antigen plays a little role in immunization when compared with the somatic antigen.