Isolation and characterization of bacterial infection hemorrhagic disease on Asian swamp eel (Monopterus albus) during nursing stage

Abstract

Motile Aeromonas species are known as one of the major pathogens causing hemorrhagic diseases in numerous aquatic animals all over the world. The hemorrhagic disease is a severe disease that causes high mortality and significant economic losses in Asian swamp eel (Monopterus albus) farms in the Mekong Delta. This study aimed to determine the bacteria causing hemorrhagic disease in Asian swamp eels during the nursing stage. Several clinical signs were observed, such as red swollen vents, abdomen hemorrhage, head edema, and hemorrhage at internal organs. All potential agents were considered, and isolated from Asian swamp eel liver, kidney, spleen on Tryptone Soya Agar and blood agar. Colonies were negative Gram, rodshaped, cream, opaque and smooth surfaces with colonies size 0.1-0.3 mm after incubating at 28°C for 24 hours. The result of 16S rRNA gene partial sequencing reconfirmed that bacteria were Aeromonas veronii. LD50 trial was carried out with A. veronii CT07 at concentrations of 103 , 104 , 105 , 106 CFU/mL in healthy Asian swamp eel with average size 9±0,9g. An experimental injection challenge study was performed and fulfilled Kochs postulates with LD50 values on A. veronii CT07 were 1.51 x 106 CFU/mL after 14 days. Moreover, clinical signs of infected Asian swamp eel similar to those observed from naturally hemorrhagic disease at farms. Using eleven antibiotics for susceptibility testing on 10 isolates that was included in the study