Enterotoxic activity of Aeromonas hydrophila and Aeromonas sobria

Two hemolytic strains of Aeromonas species isolated from the stool of adult patients with diarrhea were examined for enterotoxic activity by assays in mouse or rabbit ileal loop tests (mostly, mouse was used), suckling mice and Y1 adrenal tumor cell cultures. The strains produced enterotoxins antigenically different from each other and also from cholera enterotoxin and the heat-labile enterotoxin (LT) of Escherichia coli. The enterotoxins were cytotoxic to Y1 adrenal cells, and caused blood-stained fluid accumulation in the rabbit ileal loop test. The results suggest that two Aeromonas isolates produce cytotoxic agents but not cytotonic enterotoxins such as those produced by Vibrio cholerae and E. coll.The cytotoxin of A. hydrophila strain AK-1 and of A.sobria strain AK-2 was inactivated by heating at 56°C for 10 min. Maximal production of AK-1 toxin occurred in the early stage of growth at temperatures between 30°C and 41°C.