558 Modern Food Microbiology
gamma-interferon, and tumor necrosis factor. Superantigens are thus proteins that activate many
different T cell clones. Among the cytokines, an overabundance of IL-2 is produced,
60 and it appears
to be responsible for many or most of the symptoms of staphylococcal gastroenteritis (see below).
The activity of superantigens can be demonstrated in the laboratory by exposing murine splenocytes
to SEs. A positive response consists of T cell proliferation with concomitant production of IL-2
and gamma-interferon. The administration of IL-2 produces many of the symptoms caused by the
enterotoxin. Studies with SEC 1 concluded that SEC 1 binds to an alpha helix of MHC class II such
that the interaction between antigen-presenting cells and T cells is stabilized, leading to cytokine
production and subsequent lymphocyte proliferation.
51 The region of SEs responsible for emetic
activity is unclear although this activity has been separated from superantigenicity (see reference 81).
SEI-SEL appear to be only weakly emetic if at all.
Regarding the pathogenesis of enterotoxins in humans, many or most of the symptoms are caused
by IL-2,
60 including vomiting and diarrhea, and these symptoms can be produced by intravenous (IV)
injections.
The C-terminus of the staphylococcal enterotoxin molecules is critical to several functions. In one
study using SEB, the deletion of only nine amino acids from this region led to complete loss of T cellstimulating activity.
72 The C-terminus is believed to be critical to the three-dimensional conformation
of the SEB molecule.
72
Emetic and T cell proliferation activities can be disassociated. When SEA was altered by deletion of
three C-terminal residues, T-cell proliferation activity was retained, but the emetic activity was lost.
52
Using mutant copies of SEA and SEB, it has been shown that the MHC class II binding property alone
is not sufficient for emesis in monkeys.
45
THE GASTROENTERITIS SYNDROME
The symptoms of staphylococcal food poisoning usually develop within 4 hours of the ingestion of
contaminated food, although a range of 1–6 hours has been reported. The symptoms—nausea, vomiting, abdominal cramps (which are usually quite severe), diarrhea, sweating, headache, prostration, and
sometimes a fall in body temperature—generally lasting from 24 to 48 hours, and the mortality rate is
very low or nil. The usual treatment for healthy persons consists of bed rest and maintenance of fluid
balance. Upon cessation of symptoms, the victim possesses no demonstrable immunity to recurring
attacks, although animals become resistant to enterotoxin after repeated oral doses.
14 Because the
symptoms are referable to the ingestion of preformed enterotoxin, it is conceivable that stool cultures
might be negative for the organisms, although this is rare. Proof of staphylococcal food poisoning is
established by recovering enterotoxigenic staphylococci from leftover food and from the stool cultures
of victims. Attempts should be made to extract enterotoxin from suspect foods, especially when the
number of recoverable viable cells is low.
The minimum quantity of enterotoxin needed to cause illness in humans is about 20 ng (see the
outbreak reported in the section below). This value is derived from an outbreak of staphylococcal
gastroenteritis traced to 2% chocolate milk. From 12 cartons of milk, SEA was found at levels from 94
to 184 ng per carton, with a mean of 144 ng.
34 The attack rate was associated with the quantity of milk
consumed and somewhat with age; those aged 5–9 years were more sensitive than those aged 10–19
years. Earlier findings indicated a dose of 20–35 µg of pure SEB for adults.
88 From 16 incidents of
staphylococcal gastroenteritis, SE levels of less than 0.01–0.25 µg/g of food were found.
43
gamma-interferon, and tumor necrosis factor. Superantigens are thus proteins that activate many
different T cell clones. Among the cytokines, an overabundance of IL-2 is produced,
60 and it appears
to be responsible for many or most of the symptoms of staphylococcal gastroenteritis (see below).
The activity of superantigens can be demonstrated in the laboratory by exposing murine splenocytes
to SEs. A positive response consists of T cell proliferation with concomitant production of IL-2
and gamma-interferon. The administration of IL-2 produces many of the symptoms caused by the
enterotoxin. Studies with SEC 1 concluded that SEC 1 binds to an alpha helix of MHC class II such
that the interaction between antigen-presenting cells and T cells is stabilized, leading to cytokine
production and subsequent lymphocyte proliferation.
51 The region of SEs responsible for emetic
activity is unclear although this activity has been separated from superantigenicity (see reference 81).
SEI-SEL appear to be only weakly emetic if at all.
Regarding the pathogenesis of enterotoxins in humans, many or most of the symptoms are caused
by IL-2,
60 including vomiting and diarrhea, and these symptoms can be produced by intravenous (IV)
injections.
The C-terminus of the staphylococcal enterotoxin molecules is critical to several functions. In one
study using SEB, the deletion of only nine amino acids from this region led to complete loss of T cellstimulating activity.
72 The C-terminus is believed to be critical to the three-dimensional conformation
of the SEB molecule.
72
Emetic and T cell proliferation activities can be disassociated. When SEA was altered by deletion of
three C-terminal residues, T-cell proliferation activity was retained, but the emetic activity was lost.
52
Using mutant copies of SEA and SEB, it has been shown that the MHC class II binding property alone
is not sufficient for emesis in monkeys.
45
THE GASTROENTERITIS SYNDROME
The symptoms of staphylococcal food poisoning usually develop within 4 hours of the ingestion of
contaminated food, although a range of 1–6 hours has been reported. The symptoms—nausea, vomiting, abdominal cramps (which are usually quite severe), diarrhea, sweating, headache, prostration, and
sometimes a fall in body temperature—generally lasting from 24 to 48 hours, and the mortality rate is
very low or nil. The usual treatment for healthy persons consists of bed rest and maintenance of fluid
balance. Upon cessation of symptoms, the victim possesses no demonstrable immunity to recurring
attacks, although animals become resistant to enterotoxin after repeated oral doses.
14 Because the
symptoms are referable to the ingestion of preformed enterotoxin, it is conceivable that stool cultures
might be negative for the organisms, although this is rare. Proof of staphylococcal food poisoning is
established by recovering enterotoxigenic staphylococci from leftover food and from the stool cultures
of victims. Attempts should be made to extract enterotoxin from suspect foods, especially when the
number of recoverable viable cells is low.
The minimum quantity of enterotoxin needed to cause illness in humans is about 20 ng (see the
outbreak reported in the section below). This value is derived from an outbreak of staphylococcal
gastroenteritis traced to 2% chocolate milk. From 12 cartons of milk, SEA was found at levels from 94
to 184 ng per carton, with a mean of 144 ng.
34 The attack rate was associated with the quantity of milk
consumed and somewhat with age; those aged 5–9 years were more sensitive than those aged 10–19
years. Earlier findings indicated a dose of 20–35 µg of pure SEB for adults.
88 From 16 incidents of
staphylococcal gastroenteritis, SE levels of less than 0.01–0.25 µg/g of food were found.
43