A putative heat-labile enterotoxin expressed by strains of Aeromonas media

Fifteen isolates of Aeromonas media (seven from diarrhoeal stools, four fro m water and four from superficial skin ulcers of catfish) were examined for enterotoxin production. Ten of these isolates (six diarrhoeal, one from wa ter and three from fish) caused accumulation of fluid in the initial rabbit ileal loop (RIL) tests. Isolates from diarrhoeal stools and fish caused re latively more fluid accumulation than those from water. Those strains that caused little or no fluid accumulation in the initial experiments became en terotoxin producers after one passage through RILs, regardless of source, a nd also showed gradual enhancement of fluid outpouring after each subsequen t passage. Inocula of c. 1 x 10(4) viable cells and 0.25 ml of culture filt rate (CF) caused fluid accumulation similar to that of toxigenic Vibrio cho lerae 569B, The enterotoxic factor(s) were inactivated when held at 56 degr ees C for 20 min or 65 degrees C for 10 min and showed biological activity over a wide range of pH values. These results suggest that strains of A. me dia, whether from diarrhoeal stools, water or infected fish, are potentiall y enterotoxigenic and may have the potential to produce a heat-labile and p H-stable diarrhoeagenic factor in the same way as other known heat-labile a nd pH-stable enterotoxins.