Psychrotolerant species from the Bacillus cereus group are not necessarilyBacillus weihenstephanensis

Twenty-six strains of Bacillus cereus from different sources were determine d to be either mesophilic or psychrotrophic by growth at 6 and 42 degreesC. The strains were also screened by two polymerase chain reaction (PCR) meth ods designed to discriminate between mesophilic and psychrotrophic types. S eventeen of the 26 strains were able to grow at 6 degreesC. but only four c onformed to the new psychrotolerant species Bacillus weihenstephanensis. Am ong the 26 strains were two which caused outbreaks of food poisoning in Nor way, and three others that were isolated from food suspected of causing ill ness. The presence of the gene components encoding production of enterotoxi ns Nhe, Hbl, EntT and a recently described cytotoxin K was determined by PC R. All the strains possessed genes for at least one of these toxins, and 19 of the 26 strains were cytotoxic in a Vero cell assay. We conclude that th ere are psychrotrophic B. cereus strains which cannot be classified as B. w eihenstephanensis, and that intermediate forms between the two species exis t. No correlation between cytotoxicity and the growth temperature of the st rains was Found. (C) 2001 Published by Elsevier Science B.V. on behalf of t he Federation of European Microbiological Societies.