الفهرس 
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Abstract
The current thesis was aimed to molecular characterization of R. anatipestifer from ducklings and testing their susceptibility to antimicrobial agents as well as detecting their virulence potential and the choice for the best vaccination programme. The current study included livers, spleens, lungs, hearts and nasal swabs of 60 ducklings collected from different farms at Dakahlia Governorate, Egypt was subjected to bacteriological examination for the presence of R. anatipestifer. The overall prevalence of R. anatipestifer was 11.67% (7/60), livers and nasal swabs was 3.33% (2/60) and 8.33% (5/60) respectively. All samples were subjected to conventional culture techniques for isolation of R. anatipestifer and confirmed by PCR assay targeting gyrB gene. PCR assay was successfully amplified gyrB from all suspected isolates. In addition, the isolated strains were tested for the presence of four virulence genes namely ompA, prtC, hagA, and sspA. Genes have been detected among all seven R. anatipestifer isolates, while, sspA was detected in 5 strains. The antibiogram revealed that the organisms were sensitive to imipenem, amikacin, and rifampin, while, high resistance to ampicillin, penicillin, cefepime, trimethoprim /sulfamethoxazole, gentamicin, ceftazidime, streptomycin and cefoperazone. The revealed sequences of gyrB gene were subjected to phylogenetic analysis and compared with published sequences and the results showed that the PCR product showed 100% identity. I/P vaccination of ducklings (one week old) with 0.5ml (106 CFU/ml) of formalized inactivated vaccine raised the antibody titre in serum at 2nd week as well as 3rd & 4th weeks post vaccination comparing with before vaccination and provided the best protection against challenge up to 5 weeks of age. Results of the current study concluded that gene sequencing and phylogenetic analysis is considered one of the best methods for proper identification of R. anatipestifer. Aminoglycosides and Carbapenems are the drug of choice in treatment of such bacterium. Preparation of formalized inactivated vaccine to obtain prolonged protection.