Abstract: Background and Objective: Bacterial pathogens are the causative agents of most serious disease problems in both wild and cultured fish causing mortalities and severe economic losses. In spring 2016, mass mortality occurred in some fish farms with different salinity levels in Damietta governorate, Egypt. This study aimed to isolate and characterize pathogenic Aeromonas hydrophila (A. hydrophila) that naturally infect Oreochromis niloticus (O. niloticus) and Sparus aurata (S. aurata). Materials and Methods: Sixteen presumptive motile Aeromonas were isolated from samples of liver and kidney of O. niloticus and S. aurata on selective medium. Some isolates were identified by API 20NE and 16S rRNA, their phenotypes and multiple antibiotic resistance (MAR index); in addition, blood chemistry and histological changes in the liver, kidney and spleen of O. niloticus were investigated after infection with A. hydrophila. Results: Isolates, aer114 and aer8 were identified by 16S rRNA and submitted in GenBank under the accession numbers LC208788 and LC208789 and they exhibited degrees of virulence (71.4 -76.2%) for O. niloticus post intraperitoneal injected which showed significant increase (p<0.05) in the activity of serum AST and ALT, creatinine and urea levels but significant decreases (p<0.05) in total protein, albumin and globulin concentrations. The major histopathologic findings of infected O. niloticus were lipid vacuoles, pyknotic nuclei and necrosis in hepatocytes, while kidney showed necrosis area and hemorrhage between renal tubules but spleen showed necrosis and infiltration of fibroblasts around damage blood vessels and hemolytic between red pulps. In addition, the tested isolates showed resistant patterns of 66.6% (16/18) for many antibiotics (18), while MAR index was 0.16. Conclusion: It was concluded that the negative effects of aer114 isolated from O. niloticus on organs histology and blood examinations were more than the isolate aer8 that was isolated from Sparus aurata.
Manal Ibrahim El-Barbary , 2017. Serum Biochemical and Histopathological Changes Associated with Aeromonas hydrophila Isolated from Oreochromis niloticus and Sparus aurata with Multiple Antibiotic Resistance Index. Journal of Biological Sciences, 17: 222-234.