A study on the biological and immunological characteristics of Listonella anguillarum and Vibrio vulnificus extracellular products

Two fish pathogens, namely Listonella anguillarum (Vibrio anguillarum) and Vibrio vulnificus, which were beta-haemolytic, hemagglutinating with 1% D-mannose and hydroxamate siderophore producer were used in this study. The extracellular products (ECPs) of both species were of high enzymatic and haemolytic activities. SDS-PAGE analysis of ECPs of L. anguillarumand V. vulnificus revealed 4 band (20.7 to 47.5kDa) and 2 bands (30.1 to 46kDa) respectively. The cumulative mortalities in O. niloticus produced by crude ECPs of L. anguillarum (0.2ml/fish; 2.4mg protein /ml) and V. vulnificus (0.2ml/fish; 1.6mg protein /ml) were 90% and 80%. Heat treatment of ECPs of L. anguillarum and V. vulnificus at 56°C for 30 min reduced the mortalities to 30% and 20%, respectively. LD50 values in O. niloticus using crude and heat treated ECPs of L. anguillarum were 1.7 and 3.9 ^g protein/g fish; while those of V. vulnificus were 1.34 and 2.8 ^g protein /g fish, respectively. Injection of levamisole at a dose of 5mg/Kg fish, concurrently with ECPs of L. anguillarum and V. vulnificus resulted in subsidence of the mortality percentages from 90 to 40 and from 80 to 30, respectively. Ten laying hens were immunized with ECPs of L. anguillarum for preparation of specific egg immunoglobulins. The total protein content of IgY preparations collected from eggs of hens immunized with ECPs of L. anguillarum reached its peak 2 weeks post 3rd booster dose (3.820 ± 0.0700 g/dl). The molecular weight of separated protein bands of IgY preparations ranged from 183-191kDa. Fish injected (I/P) with specific anti ECPs IgY of L. anguillarum (4 mg/ fish) followed by I/P injection of ECPs of L. anguillarum (0.2 ml/fish; 2.4 mg protein /ml) showed a 10% mortality rate, while those challenged after receiving specific anti ECPs (100 mg/ kg B.W. orally) showed no mortalities.