الفهرس 
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Abstract
Swollen head syndrome is considered to be an important avian disease in various countries. This syndrome has caused considerable losses in the avian industry because it is responsible for mortality of 3to 4% of the birds and for reduction of 2 to 3 % at the egg production. In the present study, the prevalence of swollen head syndrome was studied in 500 broiler chickens, of which 100 were suffering from swollen head syndrome with an incidence of 200%. Identification of the causative bacterial agents was conducted focusing on E. coli, pseudomonas, klebsiella and Salmonellae isolates. The bacteriological examination revealed that out of 100 samples, 92 bacterial isolates were recovered (92%), of which 72 samples (72%) had single bacterial isolates while 20 samples (20%) had mixed two bacterial isolates. Among the recovered isolates, E. coli was the most prevalent isolate (n=80; 71.4%) followed by Pseudomonas (n=24; 21.4%), Salmonella spp. (n=4; 3.6%) and Klebsiella species (n=4; 3.6%). Antibiogram of E. coli isolates showed high sensitivity against fosfomycine while they were highly resistant to the other antimicrobials. Pseudomonas isolates showed a high sensitivity against aztreonam while they were highly resistant to the other antimicrobials. Also, Klebsiella isolates showed a high sensitivity against fosfomycine while they were highly resistant to the other antimicrobials. Meanwhile, Salmonella isolates showed high sensitivity to aztreonam while they were highly resistant to the other antimicrobials. All bacterial isolates in this study (E. coli, Pseudomonas, Klebsiella and Salmonellae isolates) showed MDR for three or more antimicrobials of different categories. PCR was applied on 7 MDR E. coli isolates to detect 5 resistance-associated genes (qnrA (0%), qnrB (0%), blaTEM (100%), blaSHV (28.6%) and TetA(A) (100%)), Also 2 virulence-associated genes (iss (100%) and CFAI (0%)) and pathotyping genes (chuA (100%) and TspE4C2 (57.14%)). PCR was applied on 4 MDR Pseudomonas isolates to detect 5 resistance-associated genes (qnrA (0%), qnrB (0%), blaTEM (100%), blaSHV(0%) and TetA(A) (100%)), 5 virulence-associated genes (mexR (100%), arr (50%), toxA (100%), phzM (0%) and ecfX (100%)). PCR was applied on 2 MDR klebsiella isolates to detect 5 resistance-associated genes (qnrA (0%), qnrB (0%), blaTEM (100%), blaSHV (50%) and TetA(A) (100%)), 3 virulence-associated genes (iutA (100%), fimH and rmpA were 0%). PCR was applied on 2 MDR salmonella isolates to detect 5 resistance-associated genes (qnrA and qnrB were 0%, blaTEM (100%), blaSHV and TetA (A) (100%)), 5 virulence-associated genes (pefA (0%), hilA (100%), ompA (100%), fimH (0%) and adrA (100%)).
In conclusion, the data of the present study showed that new serovars of Salmonella were recovered from poultry. These Salmonella serovars were found to harbor many virulence encoding genes. These serovars expressed variable degrees of resistance to antibiotics and this requires regular monitoring of the isolated Salmonella for their antimicrobial susceptibility especially that of zoonotic importance.