Production of haemolysin and enterotoxin by Aeromonas jandaei and Aeromonas trota strains after animal passage.

Five Aeromonas jandaei and 12 Aeromonas trota isolates were tested for the production of haemolysin and enterotoxin, and the correlation between these two properties. The majority (10 isolates) of the strains produced beta-haemolysis. The titres of haemolytic activity for both species were 8-64 HU/mL. In the initial ileal loop test, only two (A. trota) of the 17 isolates produced enterotoxin. One each of these 2 A. trota strains was beta-haemolytic and non-haemolytic. The remaining isolates of A. trota and A. jandaei included alpha-, beta- and non-haemolytic strains, and failed to cause any fluid accumulation in the initial tests, but did so after one-to-five sequential passages through the rabbit ileal loops. Three alpha- and 4 non-haemolytic strains switched over to the production of beta-haemolysis when they showed the positive ileal loop reaction. However, on repeated subcultures or on storage in the laboratory, all of them reverted back to their original alpha- or non-haemolytic character and no longer produced enterotoxin.