Characterisation of Aeromonas hydrophila extracellular products with reference to toxicity, virulence, protein profiles and antigenicity

摘要

A comparison of extracellular products (ECP) from a variety of Aeromonas hydrophilo isolated from fish, with LD_(50) values between 2.3 X 10~5 and 3.5 X 10~8 CFU ml~(-1), was conducted using SDS-polyacrylamide gel electrophoresis. Differences were observed in the silver stain profiles of the ECP preparations, while the total amount of protein obtained from each isolate were very similar (0.14-0.15 mgml~(-1)). Levels of toxicity for the different ECP preparations were determined through intraperitoneal injection (0.2 mgmlq) of fingerling hybrid catfish (Clarias gariepinus X Clarias macrocephalus). The ECP preparation from the high virulence isolates produced 100% mortality in all fish within 18 h of injection, while the ECP from the low virulence isolates produced 100% mortalities after 96 h. The cytolytic enterotoxin was partially purified by chromatography, and this was then used to immunise a rabbit and a catfish. Antibody titres of 1/1,024 and 1/32,768 were obtained through an indirect enzyme linked immunosorbent assay, for the catfish and rabbit sera, respectively. Purified enterotoxin from bacteria with LD_(50) values around 10~5 CFU ml~(-1) contained a strong band at 52 kDa, while one of the avirulent isolates with an LD_(50) value around 10~8 CFUml~(-1) contained a strong band at 45 kDa. The 52 kDa molecule was identified only by the catfish serum in the enterotoxin prepared from virulent isolates of A. hydrophila.