In rice, milk, and brain-heart-infusion cultures, 17 of 67 Bacillus cereus strains produced a heat-stable toxin causing morphological changes in cultures cells. All of the positive strains were associated with illness, eight with the emetic syndrome. Time-temperature studies indicated that toxin production was optimum at 25 to 30°C after 18 h in shaking culture, but low levels were produced at 15°C. Effects in cells included granulation, vacuole formation, cell rounding, acid production, and arrested cell multiplication. Of seven cell lines tested, Int 407, CHO, and HEp-2 were equally the most sensitive with the former being preferred for ease of interpreting results. The observed toxin had a molecular weight of about 14,000 and a pI of 5.9 as determined by Superose 12 chromatography and Mono P ion-exchange chromatofocusing, respectively.

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