Gene expression and histopathological changes of Nile tilapia (Oreochromis niloticus) infected with Aeromonas hydrophila and Pseudomonas fluorescens

Hepcidin, interleukin 1-beta (IL-1 beta), and cytochrome P450 1A (CYP1A) genes play an important role in the adaptive immune system in fish. To our knowledge, this is the first observation among the expression level of these genes in response to infection with Aeromonas hydrophila and Pseudomonas fluorescens in Nile tilapia (Oreochromis niloticus). Also, the effect of these experimentally induced infections was investigated regarding the mortality rate, clinical signs, and histopathological changes in the liver and kidney tissues. Three experimental fish groups were injected intraperitoneally (IP) by 0.1 ml of phosphate-buffered saline, two of these groups were injected by 0.1 ml of 1 x 10(5) CFU/ml of the suspension of either A. hydrophila or P. fluorescens. The infected groups showed extensive skin hemorrhages, cloudiness of eyes, protrusion of the scales, and severe swelling of the abdomen with inflammation of the vent and the mortality rate (MR%) was 42.75 and 37.5% in A. hydrophila and P. fluorescens groups, respectively. The histological changes of the infected O. niloticus with A. hydrophila and P. fluorescens showed fibrosis, karyolitic necrosis, the disappearance of hepatocytes wall and deposits of hemosiderin in the liver, while kidney showed dilation in Bowman's spaces, disconnection of renal tubules and hemorrhage and necrotic areas between them besides the accumulation of hemosiderin. The relative expression levels of hepcidin were higher after A. hydrophila than P. fluorescens infection in most studied organs while other studied genes expression levels were varied between infected fish groups. The relative expression of hepcidin was increased in the liver, blood, pituitary, kidney, and ovary while IL-1 beta transcripts were increased in the liver, kidney, muscle, gill, brain, and blood. CYP1A transcripts were increased in the liver, kidney, gill, and testis. The magnitude of the increase in IL-1 beta levels differed from that observed for the hepcidin and CYP1A genes. The relative expression levels of studied genes were significantly increased in the liver followed by the kidney. No significant differences were observed in the relative expression of studied genes among the gill, blood, brain, and pituitary and among the ovary, testis, brain, and pituitary during the bacterial challenge (p < .05). These findings in response to pathogen challenge could improve our understanding of the defense mechanism of adaptive immunity genes in O. niloticus organs.