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Both syndromes are caused by distinct enterotoxins (Table 7.2). A
number of toxins have been associated with the diarrhoeal syndrome but
illness appears to be associated primarily with production in the gut of
two three-component enterotoxins: a haemolytic enterotoxin HBL con-
sisting of three proteins B, L 1 and L 2 and a non-haemolytic enterotoxin
NHE. Some strains produce both HBL and NHE though others contain
the genes for only one. The toxins, which are sensitive to heat and
proteolytic enzymes such as trypsin and pepsin, are produced in the late
exponential/early stationary phase of growth. LikeC. perfringenstoxin,
they exert their effect by binding to epithelial cells and disrupting the
epithelial membrane, though the precise mechanisms of action are
thought to be different. Though the toxins can be produced in food,
their sensitivity to low pH and proteolysis, and the relatively long
incubation period associated with illness indicate that toxin production
in the gut is primarily responsible for the observed symptoms.
The emetic toxin, cereulide, is a 1.2 kDa cyclic peptide that is acid and
heat resistant. Closely related to the potassium ionophore valinomycin,
cereulide is a dodecadepsipeptide consisting of three repeats of a unit
containing 2 aminoacids and 2 oxyacids (D-O-Leu-D-Ala-L-O-Val-L-
Val) 3 (Figure 7.1). The toxin is produced in the food in the late expo-
nential to stationary phase of growth and is thought to act by binding to
and stimulating the vagus nerve.
Pathogenic features of the illness caused by the otherBacillusspp. are
not known. The short incubation periods recorded in outbreaks (from

Table 7.2 Chatacteristics of the two types of disease caused byBacillus cereus

Diarrhoeal syndrome Emetic syndrome

Infective dose 105 –10^7 (total) 105 –10^8 (cells g
^1 )
Toxin produced In the small intestine of the host Preformed in foods
Type of toxin Protein(s) 3 components
MW37, 38, 46 kDa

Cyclic peptide MW 1.2 kDa

Heat stability Inactivated 56 1 C, 5 min Stable 126 1 C, 90 min
pH stability Unstableo4 and 411 stable 2–11
Incubation period 8–16 h (occasionally 4 24 h) 0.5–5 h
Duration of illness 12–24 h (occasionally several
days)

6–24 h

Symptoms Abdominal pain, watery
diarrhoea and occasionally
nausea

Nausea, vomiting and
malaise sometimes
followed by diarrhoea,
due to additional
enterotoxin production?
Foods most
frequently
implicated

Meat products, soups,

vegetables, puddings/sauces

and milk/milk products

Fried and cooked rice,

pasta, pastry and

noodles

Adapted from Granum and Lund,FEMS Microbiol. Lett., 1997, 157 , 223 – 228

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