Inhibitory activity of antibiotic producing bacteria aganinst aeromonas hydrophila infection in oreochromis niloticus

The present study was planned to: 1) Isolate a pathogenicstrain of A. hydrophila from naturally diseased 0. niloticus and thenevaluate the pathogenicity of the isolated strain throughexperimental infection to apparently healthy 0. niloticus. 2) Isolateand select antagonistic Bacillus species from the gastrointestinaltract of apparently healthy 0. niloticus based on in-vitroantagonistic test against A. hydrophila. And then test the safety ofthe isolated antagonistic Bacillus species to apparently healthy 0.niloticus. 3) Evaluate the effect of the dietary application ofantagonistic Bacillus species (1.0 X 107 cfu/g diet) on the immuneresponse and resistance of 0. niloticus to A. hydrophila infectionafter two feeding periods (15 and 30 days). Also the viability of theBacillus species in the prepared feed was examined weekly afterstorage at refrigerator and at room temperature for up to 6 weeks.The results can be summarized as follows:A pathogenic strain of A. hydrophila was isolated from naturallydiseased 0. niloticus showed signs of haemorrhagic septicemia.The pathogenicity of the isolated strain revealed that intra-peritoneal inoculation of A. hydrophila (0.5 X 108 cfu/fish) intoapparently healthy 0. niloticus induced 90% mortality amongthe inoculated fish. The observed signs and P IM findings on theexperimentally infected fish were similar to that recorded onnaturally diseased fish, including darkening skin, signs ofhemorrhagic septicemia, hyperemia and hemorrhage at differentparts of the body, scales losses, skin erosions, fin rot andabdominal distension (ascites