الفهرس 
DedicationOnly 14 pages are availabe for public view
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Abstract
In the present study, molecular identification of obtained Salmonella isolates was carried out by using Polymerase Chain Reaction (PCR) through detection of invA gene by using specific primers targeting invA gene. The results revealed that all examined Salmonella isolates are positive for the presence of invA gene and the molecular weight of amplified product was 284bp.
In this study, molecular typing of 15-Salmonella isolates was represented in two serotypes, the first one including Salmonella typhimurium (14 isolates) and second serotype was Salmonella infantis (one isolate) with a percentage of (14/15) 93.3% and (1/15) 6.7%, respectively.
In the present work, all isolates were completely sensitive (15/15, 100%) to amikacin, Sulphamethoxazole / trimethoprim, ciprofloxacin and enrofloxacin. Isolates responded variably to tetracycline and oxytetracycline (13/15, 86.7% of each), doxycycline and gentamicin (12/15, 80% of each), chloramphenicol and ampicillin (9/15, 60% of each) and colistin sulfate (20%). They had intermediate sensitivity to neomycin (11/15, 73.3%), streptomycin (5/15, 33.3%), Ampicillin (2/15, 13.3%), and (1/15, 6.7%) for doxycycline and chloramphenicol.
All isolates were completely resistant (15/15, 100%) to cephradine and amoxicillin, while they showed a variable resistance to colistin sulfate (12/15, 80%), streptomycin (9/15, 60%), chloramphenicol (5/15, 33.3%), ampicillin and neomycin (4/15, 26.7% of each), gentamicin (3/15, 20%) and (2/15, 13.3%) for tetracycline, oxytetracycline and doxycycline.
In our study, the Minimum Inhibitory Concentration of eight represented (7) S. typhimurium serotypes and (1) S. infantis serotype to nine antibacterial agents indicated that examined Salmonella serotypes were completely sensitive to doxycycline and colistin sulfate while, variable degree of resistance to the other tested antibacterial agents and the examined serotypes were completely resistant to sulphaquinoxalin.
In the present study, Conventional Polymerase Chain Reaction (PCR) used for molecular identification of some resistance genes against different antibacterial agents [Sul-1, bla TEM and floR] using specific primer for each gene showed that the incidence of these resistance genes in the examined isolates was (100%) for sul-1, (73.3%) for bla TEM and (46.7%) for floR. The results of Multiplex Polymerase Chain Reaction (m-PCR) for molecular identification of (streptomycin resistance genes) using specific primers indicated that the incidence of strA-strB and aadA were (73.3%) and (66.7%), respectively.
In this study, two inactivated Salmonella bacterins, one of them locally prepared from Salmonella infantis and the other was commercial servac trivalent containing (S. typhimurium, S. enteritidis and S. kentucky) passed all the quality control requirements. The protective efficacy of the two inactivated bacterins had been studied in ducks and showed that the protection rates after 28day post challenge orally with the virulent isolates of S. typhimurium and S. infantis were 100% for all vaccinated groups while, 40% for unvaccinated group.
In the present study, the rate of fecal shedding was 40%, 20%, 0%, 20%, 80%, 40% and 60% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for the vaccinated group with Commercial servac trivalent bacterin challenged with S. typhimurium. While, the rate of fecal shedding was 60%, 20%, 0%, 0%, 20%, 0% and 20% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for the vaccinated group with commercial trivalent servac bacterin challenged with S. infantis. While, the rate of fecal shedding was 0%, 80%, 0%, 60%, 20%, 20% and 40% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for vaccinated group with S. infantis inactivated bacterin and challenged with S.typhimurium. While, the rate of fecal shedding was 20%, 20%, 0%, 20%, 80%, 20% and 40% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for vaccinated group with S. infantis inactivated bacterin and challenged with S. infantis. 100%, 60%, 100%, 60%,50%, 50% and 50% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for (unvaccinated) challenged group with S. typhimurium. While, the rate of fecal shedding was 100%, 80%, 0%, 60%, 60%, 20% and 40% at 1st, 3rd, 5th, 7th, 14th, 21st and 28th day post challenge for (unvaccinated) challenged group with S. infantis.
In our study, the rate of re-isolation of Salmonella from different organs of vaccinated and (unvaccinated) challenged ducks were showed that Salmonella were isolated from heart blood, liver, spleen and ceca at rates of (0%), (0%), (0%) and (30%), respectively for the vaccinated group with Commercial trivalent bacterin challenged with S. typhimurium but at rates of (10%), (10%), (0%) and (20%), respectively were noticed for vaccinated group with Commercial trivalent vaccine challenged with S. infantis. At rates of (20%) from heart blood, liver, spleen and ceca for vaccinated group with locally prepared inactivated S. infantis bacterin and challenged with S. typhimurium but at rates of 0%, 0%, 0% and 20%, respectively were recorded for vaccinated group with locally prepared inactivated S. infantis bacterin and challenged with S. infantis, while at rates of (100%), (60%), (40%) and (80%), respectively for unvaccinated (challenged) group with S. infantis and at rates of (100%), (100%), (80%) and (90%), respectively for the other unvaccinated (challenged) group with S. typhimurium.
In the present study, there were no significant differences in body weight gain between all groups including the negative control group before challenge. While, at 4th week post challenge, unvaccinated challenged groups showed significant reduction in body weight compared to the negative control group and vaccinated groups resulted in no significant reduction in body weight compared to the negative control group at the end of experiment.
In this study, clinical signs and post-mortem lesions of the experiment after challenge showed that both groups receiving locally prepared inactivated S. infantis bacterin and the commercially servac trivalent inactivated bacterin were 100% protected from clinical signs and mortality after challenged with virulent S. typhimurium and S. infantis after 28-day post challenge. All vaccinated and negative control groups remained normal during the course of experiment. Birds in the negative control group (neither vaccinated nor challenged) did not manifest any signs of disease throughout the trial period.
All birds in the positive control groups (G3a) and (G3b) (unvaccinated and challenged) displayed clinical signs include loss of appetite, ruffled feathers, dullness, emaciation, huddling together, dropped wings, closed eyes (sleepy appearance), whitish diarrhea, thirsty, nervous signs (tremors of head and neck), staggering gait and lameness. Post-mortem lesions were general septicemia, severe congestion of intestine, enlarged gall bladder, (spleen, heart and liver) are congested and enlarged with hemorrhagic patches, airsacculitis and also kidneys were enlarged and congested.