Environment driven cereulide production by emetic strains of Bacillus cereus

The impacts of growth media and temperature on production of cereulide, the emetic toxin of Bacillus cereus, were measured for seven well characterised strains selected for diversity of biochemical and genetic properties and sources of origin. All strains carried cereulide synthase gene, ces, on a megaplasmid of ca. 200 kb and all grew up to 48-50 degrees C, but produced cereulide only up to 39 degrees C. On tryptic soy agar five strains, originating from foods, food poisonings and environment, produced highest amounts of cereulicle at 23 to 28 degrees C, whereas two strains, from human faeces, produced cereulicle similarly from 23 to 39 degrees C, with no clear temperature trend. These two strains differed from the others also by producing more cereulide on tryptic soy agar if supplemented with 5 vol.% of blood. whereas the other five strains produced similarly, independent on the presence of blood. On oatmeal agar only one strain produced major amounts of cereulicle. On skim milk agar, raw milk agar. and MacConkey agar most strains grew well but produced only low amounts of cereulicle. Three media components, the ratio [K+]:[Na+], contents of glycine and [Na+], appeared of significance for predicting cerculide production. Increase of [K+]:[Na+] (focal variable) predicted (P<0.001) high cereulicle provided that the contents of glycine and [Na+] (additional variables) were kept constant. The results show that growth medium and temperature up and downregulate cereulicle production by emetic B. cereus in a complex manner. The relevance of the findings to production of cereulicle in the gut and to the safety of amino acids as additives in foods containing live toxinogenic organisms is discussed. (C) 2008 Published by Elsevier B.V.