Biochemical characteristics and enterotoxicity of Aeromonas species isolated from man and environment

A total of 147 isolates of Aeromonas spp., of which 54 were isolated from children and adults with diarrhoea, 44 from variety of water sources and 49 from environmental sources, were tested for enterotoxin production and its correlation with biochemical characters. Lysine was decarboxylated by 38% of A. hydrophila, 35% of A. sobria and 20% of A. caviae. Majority strains were unable to utilise citrate as the sole source of carbon except one of A. hydrophila, 8 of A. sobria and 6 of A. caviae. Beta-haemolysis was shown by 108 isolates that included 79% of A. hydrophila, 76% of A. sobria and 70% A. caviae. About 56% of Aeromonas strains including A. caviae caused fluid accumulation in the rabbit ileal loop in the initial tests and the remaining did so after 1-3 consecutive passages. Enterotoxin production did not correlate with the positive biochemical characters such as Voges-Prauskauer reaction, lysin decarboxylation, haemolysin production, citrate utilisation and failure to ferment arabinose either singly or in combination. This study indicates that enterotoxicity of Aeromonas may not be correlated with any of the biochemical characters either singly or in combination.