Relationship of toxin production to species in the genus Aeromonas

Ninety-five strains of Aeromonas were divided into three species--A. sobria, A. hydrophila and A. caviae--on the basis of results in 13 biochemical tests. The minimum number of tests necessary to distinguish these species was determined. Culture filtrate of the strains were tested for cytotoxin and cytotonin, haemolysin and protease. One filtrate with high-titre cytotoxin, haemolysin and protease activities was subjected to gel filtration on Sephadex G75 and isoelectric focussing. Of the five cell lines tested, Vero cells were most sensitive to the cytotoxin; no reproducible cytotonic effects were observed. The haemolysin effect appeared to be equivalent to cytotoxin. At least two distinct protease activities were found that might be responsible for the cytotonic effects described. Cytotoxin production was species related; it was present in A. sobria and A. hydrophila but not in A. caviae.