Effects Of Aeromonas Hydrophila On The Antibacterial Peptide Activity And The Hepcidin Gene Expression Of Monopterus Albus

Monopterus albus was one of the important freshwater fish in China. With the increase of the demand, its cultivation area increased year by year. However, with the increase of the farming area and the breeding density, the eutrophication of aquaculture waters became more and more serious. This caused culture environment deterioration and disease outbreaks,such as virus disease, bacterial diseases, fungal diseases and parasitic diseases. Especially hemorrhagic disease caused by bacteria often induced severe destruction to Monopterus albus aquaculture and seriously limited its large-scale production. Aeromonas hydrophila was one of the main bacteria that caused diseases of Monopterus albus. Antimicrobial peptides were an important part of the nonspecific immune system of fish. When damaged or invaded by pathogenic microorganism, fish body produced antimicrobial peptides quickly in order to prevent and kill pathogenic microorganisms. After been artificially infected by different concentrations of Aeromonas hydrophila, the blood cells, the antibacterial activity of the important organs extract, and the hepcidin expression quantity of Monopterus albus were investigated by the methods of microscopic measurement,acid extraction, inhibited zone, FQ-PCR and so on. The results would provide reference for further researches on the disease-resistant mechanism of Monopterus albus. The main contents and results were as follows:1. Effects of Aeromonas hydrophila on Blood Cells of Monopterus albusWith the increase of the concentrations of Aeromonas hydrophila, the concentration of erythrocytes decreased after injection 24 hours, first increased and then decreased after injection 48 hours and 72 hours, but no significant differenceswere shown. The percentage of leukocyte such as neutrophils, monocytes and lymphocytes increased obviously.2. Effects of Aeromonas hydrophila on the antibacterial activity of the important organs extract of Monopterus albusThere were no obvious antibacterial activity on Bacillus Subtilis, which came from the crude extracts of the liver, kidney, intestine and skin, respectively, after Aeromonas hydrophila injection. But there were visible antibacterial activity on Aeromonas hydrophila, Escherichia coli and Staphylococcus aureus, respectively. The antibacterial activity of the extracts from different tissues and organs were different to the same bacterium, and the antibacterial activity from the same tissues or organs varied to different bacteria. The antibacterial activity of extracts from four tissues was the highest to Staphylococcus aureus, then to Escherichia coli, and the lowest to Aeromonas hydrophila.The antibacterial activity of the skin extract was the highest to Escherichia coli,and that of the intestine was the lowest. But the antibacterial activity of skin decreased as time prolonged. The antibacterial activity of liver and kidney were higher than that of intestine and skin to Staphylococcus aureus. The antibacterial activity of kidney increased and that of skin decreased as time prolonged to Aeromonas hydrophila.3. Effects of Aeromonas hydrophila on hepcidin expression quantity of Monopterus albusThe results demonstrated that hepcidin transcripts were detected in kidney of healthy Monopterus albus. When challenged with Aeromonas hydrophila injection,the hepcidin expression quantity increased significantly. The hepcidin transcripts decreased as time prolonged in mostly tested groups, but increased in the group treated with Aeromonas hydrophila of which concentration at 1×108cfu/mL.