LC-MS analysis of the emetic toxin, cereulide, produced by Bacillus cereus.

A quantitative and chemical assay of cereulide produced in the cultures by some strains of Bacillus cereus was performed on a HPLC and a ESI electrospray ion trap mass analyzer, using the synthetic cereulide as a standard. All 20 strains of emetic B. cereus were found to produce 27 - 740 ng/ml of cereulide by the LC-MS analysis. In contrast, none of the 10 diarrheal strains produced it. 10(2) cfu/ml of the cereulide producible strain with a 210 ng/ml yield was inoculated into the 10% suspensions of 14 food products, and was incubated at 32 degrees C for 24h. The B. cereus counts in the cultures grew in the order of 10(8) to 10(9) cfu/ml, although the bacteria could not grow in fruits, and the yields of cereulide ranged from 5.18 mu g in curry to 0.03 mu g/g of raw material and/or powder material, except for fruits. These culture supernatants were also tested for the biological activity in the HEp-2 cell culture assay. Consequently, a certain correlation was shown between the yields of cereulide and the HEp-2 vacuolation activities. In addition, the supernatants were administered i.p. to 5 Suncus marinus test animals. The emetic dose was calculated to be approximately 16 mu g/kg.