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The Bacillus cereus group comprises seven species: Bacillus cereus sensu stricto, Bacillus thuringiensis, Bacillus anthracis, Bacillus weihenstephanensis, Bacillus mycoides, Bacillus pseudomycoides, and Bacillus cytotoxicus. Three members of the B. cereus group B. anthracis, B.cereus, and B. cytotoxicus are well-known human pathogens. The members of the B. cereus group produce endospores that are highly resistant to disinfectants, radiation, desiccation, and heat. All members of the group express a wide range of protein toxins such as phospholipases, hemolysins, and enterotoxins. In addition, B. anthracis, the causative agent of anthrax, produces three different proteins necessary for the development of anthrax and B. thuringiensis produce endotoxins active against insects. Members of the B. cereus group are widespread in nature and are easily spread to foods, where they may cause several types of food-associated illnesses. Due to the highly resistant spores, they are becoming increasingly important in the food industry and especially during production of sous-vide foods. In this chapter, the protein toxins expressed in B. cereus sensu stricto and B. thuringiensis are described.

Bacillus cereus causes two types of foodborne disease. During growth of B. cereus in the gastrointestinal tract, virulence factors can be produced, leading to diarrheal illness. Several toxins are suspected as virulence factors, of which the protein toxins Hbl, Nhe, and CytK have been studied the most. The emetic syndrome is an intoxication caused by preformed toxin (cereulide). Bacillus species outside the B. cereus group have been implicated in foodborne disease. Species such as Bacillus subtilis, Bacillus mojavensis, Bacillus pumilus, and Bacillus licheniformis can produce cyclic lipopeptides which show toxic activity, although their link to foodborne disease remains uncertain.

This chapter synthesizes the available knowledge on the virulence factors found in the bacterial group of Bacillus cereus sensu lato. B. cereus s.l. is a group of six species of Bacilliaceae, displaying a large virulence spectrum. B. anthracis, the causative agent of anthrax, is highly monomorphic, non-mobile, non-hemolytic, and sensitive to penicillin. These phenotypic features are used to differentiate B. anthracis from the other members of the group. The other animal pathogen, B. thuringiensis, is active against larvae of lepidopteran, dipteran, and/or coleopteran insects. These two pathogenic organisms possess a series of virulence factors specific to their hosts. B. cereus sensu stricto is an opportunistic bacterium known for its role in food infection and intoxication, but it has also been found in other habitats, including the intestinal tract of arthropods, where it forms long filaments and leaves as symbiont. In this context, it is has been named Arthromitus. B. anthracis represents a important issue because of the severity of the disease it causes. Although the inactivation of its transcriptional regulator PlcR has now been well documented, alternative regulatory pathways have been suggested. Determination of the complete genome sequences of several B. cereus s.l. will certainly permit pointing out the diversity of the virulent genes and their regulatory sequences.

The bacteria responsible for causing food poisoning have managed to adapt to the new niches presented to them with modem food processing. Much of the adaptation is through assimilation of new genes, including toxin- and invasion-related genes. The virulence factors that are responsible for the direct action on host tissues, and thereby development of disease, are dependent on the physical and genetic background of both the bacteria and the host. The toxins are, for some of thefood poisoning diseases, the only cause of the symptoms but may for others only increase the severity of the disease. This chapter explores some of these toxins that are on mobile elements and can conceivably be transferred to bacteria thathave not yet been identified as potential food pathogens. It is not sufficient for bacteria to possess genes that can encode for toxins or other virulence factors. The bacteria must also be able to survive one or a number of detrimental and changing environmental factors, including dehydration, heat, cold, low pH values (stomach), competing flora, and other intestinal defense mechanisms. There are many bacteria that carry the same or equivalent virulence genes as bacteria known to cause foodborne illness that have not yet been fully recognized as cause of a human gastroenteritis, i.e., Bacteroides fragilis and Citrobacter spp.