Comparison of biological effect of the two different enterotoxin complexes isolated from three different strains of Bacillus cereus

The cytotoxicity of the two different enterotoxin complexes of Bacillus cereus was compared after isolation from three different strains. Protein components of non-haemolytic enterotoxin (NHE) of 39 kDa, 45 kDa and 105 kDa were isolated from all of the three strains, whilst proteins B, L1 and L2 of haemolysin BL (HBL) were isolated from supernatants of two strains (F837-76 and 1230-88). These proteins were not detected in strain 0075-95. Inhibition of protein synthesis in Vero cells was used as a measure of cytotoxicity. The HBL complex from strain F837-76 was highly toxic. This strain also produced the NHE complex. However, when purified, at least two of the components of NHE had to be present in higher amounts than those of the components of HBL to cause the same degree of toxicity. Both complexes purified from strain 1230-88 were cytotoxic. The amount required to cause the same degree of cytotoxicity was approximately equal for the components of the two complexes, except that higher amounts of the 105 kDa protein of NHE had to be present than for the other components. None of the purified complexes from strain 1230-88 was toxic in amounts comparable to those of the HBL complex of strain F837-76 and NHE of strain 0075-95. These results indicate that when measuring cytotoxic enterotoxins from B. cereus at least two different complexes and six different proteins have to be taken into consideration.