Haemolysin and enterotoxin production by Aeromonas caviae isolated from diarrhoeal patients, fish and environment.

Beta-haemolytic activity was shown by 46 (63%) of the 73 Aeromonas caviae strains isolated from diverse sources, such as diarrhoeal stools, fish ulcers and water in titres of 16-64 HU/ml. Only 2 strains showed alpha-haemolytic activity and the remaining 27% of them were nonhaemolytic. Live cells and culture filtrates of 60.3% of the A. caviae isolates caused accumulation of fluid in rabbit gut loops in the initial set of experiments. Of the 46 strains showing beta-haemolytic activity only 34 gave positive ileal loop reactions in the initial experiments. One of the 2 strains showed alpha-haemolytic activity and 9 of the 20 nonhaemolytic strains also caused fluid accumulation in the same set of experiments. Those strains that showed beta-haemolytic activity caused significantly more (p less than 0.01) fluid outpouring than the alpha- or nonhaemolytic isolates regardless of their sources of origin. Twenty-nine (39.7%) strains that showed alpha-, beta-, and nonhaemolytic activity and caused little or no fluid accumulation in initial experiments did so after 1-3 consecutive passages through rabbit gut. The nontoxic strain showing alpha- and non-haemolytic activity switched over to production of beta-haemolytic activity once their live cells gave positive loop reactions. However, on repeated subcultures or on preservation in the laboratory for 2-3 weeks, all of them reverted back to their original nontoxic haemolytic types, i.e. alpha- or nonhaemolytic activity.