الفهرس 
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Abstract
Mycoplasma gallisepticum and Escherichia coli are of the most important bacterial pathogens causing disease problems commonly encountered in poultry industry where Mycoplasma gallisepticum is the etiologic agent of chronic respiratory disease of chickens and infectious sinusitis of turkeys in Egypt (El Shater1986) while Escherichia coli is the main complicating factor in this disease resulting in significant economic losses through mortality, morbidity, cost of treatment and condemnation at processing plant (Cheville and Arp,1978 and Prukner, 1986 ).
The objective of this study was to develop a locally prepared combined inactivated vaccine comprising M. gallisepticum in addition to Escherichia coli serotypes O1, O2 and O78 which is the mostly predominated in poultry infection (Rosenberger and Cloud, 1981).
Preliminary confirmation of M. gallisepticum or E. coli strains was done through identity study including morphological and biochemical identification and more confirmatory test was done by using of PCR using a specific primer for the 16 SrRNA gene of M. gallisepticum and a specific primer of Shiga toxin gene of E. coli (serotypes O1, O2 and O78) and the given PCR product was 185pb and 323 bp respectively.
When the prepared combined inactivated vaccine was tested for the sterility, it was found to be free from any contaminants either aerobic bacteria, anaerobic bacteria, Mycoplasma and fungi. As regards to safety test, it was found that chickens vaccinated with even the double doses didnꞌt show any abnormalities or adverse reaction.
Concerning the Potency testing of the prepared vaccine, the antibody titer against Mycoplasma gallisepticum after vaccination, showed a positive titer starting as early as the first week post vaccination on both groups that vaccinated with Mycoplasma gallisepticum commercial vaccine and that vaccinated by locally prepared combined Mycoplasma gallisepticum and E. coli vaccine group giving mean titers 832 and 786 respectively. The peak of antibody titers was at the 7th week post single vaccination (2487 and 2418 respectively) while the maximum level of antibody titers reached 5695 and 5600 at 8 weeks post boostering in the same chicken groups respectively.
Regarding the E. coli antibody response, the positive antibody titer against E. coli after vaccination was noticed as early as the first week post vaccination in both groups that vaccinated with either E. coli commercial vaccine or vaccinated with locally prepared combined Mycoplasma gallisepticum and E. coli vaccine giving mean titers 711 and 828 respectively. The peak of antibody titer was 2110 and 2240 and achieved at 7 weeks post single vaccination within chickens of the same groups while the maximum antibody titers level 3553 and 3689 were observed at 8 weeks post boostering within the same chicken groups respectively.
As regards to the protection percent estimated after challenge test it was 62.0% and 72.0% post single and booster vaccination against virulent M. gallisepticum R strain respectively in the chicken groups vaccinated with the locally prepared MG and E. coli vaccine while it was 65 % and 75.0% for the commercial MG vaccine at the same intervals. At the same time the protection percent estimated after challenge test was 66.67% and 77.47% post single and booster vaccination against virulent E. coli virulent strains respectively in the chicken groups vaccinated with the locally prepared MG and E. coli vaccine while it was 60% and 72.97% for the commercial E. coli vaccine at the same intervals. These protection levels were reflected in the form of lower air sac lesions corresponding to both organisms as it is clear that, air-saculitis depends on the immune status of the birds as the grads were significantly lowered after the challenge post boostering than after the challenge post first dose of vaccination. This means that the ELISA antibody titer obtained post either single or booster vaccination was correlated with such results obtained after challenge test for both organisms.
These results indicated that, the use of the Mycoplasma gallisepticum in a combined vaccine with E. coli did not retard the immune response of the birds against each other but may potentiate it and reflected in the form of good protection percent for both.
It could be concluded that the locally prepared combined MG and E. coli vaccine is of great value because it give acceptable significant levels of protection in vaccinated chickens against MG and E. coli infections in comparison with the non vaccinated chickens.
Depending on this study, it could be recommended that, the production of this vaccine will be useful to avoid MG and E. coli infections and their complications in the poultry field.