الفهرس 
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Abstract
Aeromonas species were considered as an aquatic micro-organism affecting fish and reptiles. Over the last few years, other species including poultry were affected causing many pathological conditions. Therefore, in this study 60 broiler chicken, 7 layer and 11 duck farms of different ages sufferring from diarrhea and stunted growth, were investigated, 9 broiler chicken farms yielded 14 Aeromonas isolates (7 A.caviae, 2 A.hydrophila, 3 A.schubertii and 2 A.trota), 1 layer farm yielded only one A.trota isolate and 2 duck farms produced 2 A.hydrophila isolates.
Bacteriological examination of ration and water samples of 50 poultry farms revealed Aeromonas species isolated from 11 ration samples and 6 from water samples and biochemically identified as A.caviae (3 isolates), A.hydrophila (8 isolates) from ration and A.caviae (4 isolates), A.hydrophila (2 isolates) from water.
Standard A.hydrophila, A.hydrophila and A.schubertii of fish source were obtained from microbiology and fish disease department, faculty of veterinary medicine, Cairo University to compare these isolates with those of poultry when sensitivity, PCR identification and RFLP were applied. The results revealed the following:
• Sensitivity test of poultry A.hydrophila was similar to that of standard but differed from that of the fish isolates since poultry isolates were sensitive to gentamicin, amikacin and nor-floxacin, while fish isolates were sensitive to nitrofurans, chloramphenicol, sulpha-trimethoprim and ampicillin-sulbictam.
• Similarity in sensitivity of poultry and fish A.schubertii isolates to gentamicin, amikacin and nor-floxacin and differences in sensitivity was to chloramphenicol, cephalocin, colistin, nitrofurans, ciprofloxacin and ampicillin-sulbictam.
• A.hydrophila isolates were more resistant to antibiotics than the other Aeromonas species followed by A.caviae, A.trota then A.schubertii .Also A.hydrophila isolates from fish and poultry were more resistant to antibiotics than those from water.
• Polymerase chain reaction was standardized for the identification of biochemically identified poultry Aeromonas, standard and fish isolates using specific primer 16S rRNA gene, elctrophoretic analysis of the PCR product revealed the specific amplification of 599 bp fragment for all selected Aeromonas isolates.
• RFLP of 16S rRNA gene using Mbo1 and Alu1 restriction enzymes resulted in similarity among poultry, standard and fish isolates.
• 16S rRNA gene of A.hydrophila, A.caviae and A.schubertii was digested with Mbo1 only, while that of A.trota was digested with both Mbo1 and Alu1.
Results of pathogenicity test for A.hydrophila, A.trota, A.caviae and A.schubertii were recorded as the following:
• Mortality was 13.3% in A.hydrophila, 20% in A.trota, 13.3% in A.caviae and 6.7% in A.schubertii infected groups.
• non-significant decrease in body weight till the end of experiment in A.hydrophila infected group and a significant decrease from 3rd to 5th week post infection in A.trota , A.caviae and A.schubertii infected groups.
• A.schubertii infection induced marked effect on body weight than A.caviae, A.trota and A.hydrophila.
• On histopathology, small intestine showed focal desquamation associated with inflammatory cells infiltration and oedema in the lamina propria, also liver showed dilatation, congestion and haemorrhage in portal vein, hepatic sinusoid and bile duct with inflammatory cells infiltration in the portal area and hepatic parenchyma, while lung showed congestion in stromal blood vessels with perivascular oedema and haemorrhage associated with bronchiolar mucosal ulceration, in addition to kidney showed haemorrhage and inflammatory cells aggregation in between the degenerated tubules and finally spleen showed congestion, haemorrhage, nodules formation and necrosis.