A new cytotoxin from Bacillus cereus that may cause necrotic enteritis

A cytotoxin (CytK) has been isolated from a Bacillus cereus strain that cau sed a severe food poisoning outbreak killing three people. A protein of 34 kDa was highly cytotoxic, and the addition of other secreted proteins gave no synergistic effect. CytK was also necrotic and haemolytic. No known B. c ereus enterotoxins were produced by this strain. A DNA sequence from 1.8 kb upstream to 0.2 kb downstream of the toxin gene was sequenced. The deduced amino acid sequence of the toxin showed similarity to Staphylococcus aureu s leucocidins, gamma -haemolysin and alpha -haemolysin, Clostridium perfrin gens beta -toxin and B. cereus haemolysin II, all belonging to a family of beta -barrel channel-forming toxins. There was no sequence similarity betwe en CytK and enterotoxins of B. cereus. The upstream sequence contained a pa rtial sequence of a putative histidine kinase gene. A recognition site for PlcR, which regulates the transcription of enterotoxins HBL and Nhe of B. c ereus, was found in the promoter region of the toxin. This new cytotoxin ma y be responsible for a disease that is similar to, although not as severe a s, the necrotic enteritis caused by the beta -toxin of C. perfringens type C.