Enterotoxicity of Aeromonas hydrophila: skin responses and in vivo neutralisation

Culture filtrates and partially purified enterotoxins of 6 strains of Aeromonas hydrophila isolated from faeces of diarrhoeic and healthy persons, drinking water, sewage and faeces of domestic animals caused induration and increased capillary permeability in skin of adult albino rabbits. The activities were less in crude enterotoxins indicating partial loss during purification. Heat treatment for 30 min at 60 degrees C and 56 degrees C inactivated the induration and permeability effects of culture filtrates and crude enterotoxins respectively. The activities were most pronounced at pH 8.0 showing gradual loss of activities at lower pH values disappearing completely in culture filtrates at 3.0 and in crude toxins at 4.0. The induration and permeability factor activities of crude enterotoxin were neutralised proportionally in vivo with antitoxin raised against the same in rabbits. Suppression effect was more when antitoxin was injected prior to inoculation of toxin. This study demonstrates that the assay of the activity of skin permeability factor being an easier process than loop test, may be used for assay of enterotoxin of A. hydrophila.