Abstract
Pseudomonas aeruginosa is a G-ve bacterium causing diseases threat the animals, poultry and fish resources. Recently medical plants are greatly used as replacements for antibiotics in diseases treatment of both avian and animals The present study was carried out to evaluate the effect of dietary supplementation of yucca extract on growth performance and diseases resistance of Nile tilapia challenged with pseudomonas aeruginosa which previously isolated. Total number of two-hundred and twenty O.niloticus fish were used in our work (70 diseased fish for isolation of Pseudomonas aeruginosa and 150 apparently healthy fish for experimental design). One-hundred and fifty fish in the experiment were divided into five groups, 30 fish each and fed on five experimental diets (first group received basal diet(control –ve), second group received basal diet and infected with pseudomonas aeruginosa in a dose of 3x107cfu/ml at the end of the experiment(control +ve). Third group received basal diet with 0.1% yucca extract and infected with pseudomonas aeruginosa, fourth group received basal diet with 0.14% yucca extract and infected with pseudomonas aeruginosa, fifth group received basal diet with 0.2% yucca extract and infected with pseudomonas aeruginosa). Results of this study showed a higher growth performance for 0.1% yucca group with significant differences with control, 0.14% and 0.2% groups. A total of 10 pseudomonas aeruginosa strains were isolated from 70 diseased fish samples with a percentage of 14.28%. The isolated strains from examined fish were identified by cultural, morphological, biochemical characters and PCR technique. The results of PCR examination revealed that all 10 isolated strains were positive for the specific gene of pseudomonas aeruginosa (16S rDNA) . Also the PCR results revealed that, opr L and exo S virulence genes were detected in all ten studied strains . Our results after experimental challenge showed that the re-isolation and mortality rate decreased in groups fed on yucca extract than the control group and the best survival was observed in group fed on 0.1% yucca extract. These results concluded that the optimum dietary Yucca extract inclusion level in the diet of Nile tilapia could be 0.1% as a feed additive to promote growth and increase disease resistance.

Key words: Yucca extract, growth performance, Pseudomonas aeruginosa, virulence genes, Oreochromis niloticus.