Page 801 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

760 SECTION | XI Bacterial and Cyanobacterial Toxins

VetBooks.ir and they are best described as short proteins secreted by TOXICITY
the cell into the growth matrix (Balaban and Rasooly,
The symptoms of staphylococcal food poisoning occur in
2000). All SE types are water soluble, very heat resistant,
and resist most proteolytic enzymes, such as trypsin and humans when as little as 100 ng of enterotoxin is ingested
(Bennett, 2005). There is a paucity of information on the
pepsin, which make it possible for them to travel through
dose of individual enterotoxins that will cause clinical
the digestive tract to their site of action. Thus, all SE
signs in common domestic animals. The first and most
types resist the conditions that could easily destroy the
common clinical sign in dogs is vomiting, which usually
bacteria that produced them. SEs are thought to have a
occurs within 2 or 3 h following ingestion. This can often
direct effect on the intestinal epithelium and on the vagus
suffice to remove enough contaminated food from the
nerve to cause stimulation of the emetic center as well as
gastrointestinal tract to prevent the development of more
increasing peristalsis. Foods that are frequently associated
severe clinical signs. However, vomiting can be pro-
with staphylococcal food poisoning include meat and
tracted and lead to fluid and electrolyte abnormalities.
meat products; poultry and egg products; salads such as
Diarrhea can often develop within 2 48 h following
egg, tuna, chicken, potato, and macaroni; bakery products
ingestion of contaminated food and can be severe, some-
such as cream-filled pastries; and milk and other dairy
times bloody. The combination of both vomiting and diar-
products. An example of a proverbial high-risk food is the
rhea in the affected animal can quickly lead to profound
potato salad at a summer picnic left out for several hours
fluid and electrolyte abnormalities. The animal may
without refrigeration.
exhibit tenderness to the abdomen or the stomach and the
B. cereus is in the family Bacillaceae, which are all
intestinal tract can be distended with gas (Coppock and
Gram-positive rod-shaped bacteria that form endospores.
Mostrom, 1986).
The family has two main divisions: the anaerobic spore-
The emetic form of B. cereus food poisoning is char-
forming bacteria of the genus Clostridium and the
acterized in humans by an acute attack of nausea and
aerobic or facultatively anaerobic spore-forming bacte-
vomiting, which occurs within 1 5 h after consumption
ria of the genus Bacillus. B. cereus is a primary inhabi-
of contaminated food. Diarrhea is not a common feature
tant of soils and contaminates almost all agricultural
in this type of illness. In humans, the diarrheal syndrome
products. It is also routinely involved in the contamina-
is characterized by abdominal pain, abdominal cramping,
tion and spoilage of food products. B. cereus can also
and diarrhea that often can be very watery. There is an
be involved in wound, eye, or systemic infections.
incubation period of 4 16 h, and clinical signs can persist
B. cereus food poisoning is generally described as
for 12 24 h. Nausea may accompany the diarrhea, but
having two types of illness caused by different metabo-
vomiting rarely occurs.
lites. The diarrheal type of illness is caused by one or
Testing for enterotoxins requires specialized labora-
several heat-labile, high-molecular-weight proteins,
tory techniques and methods of detection have greatly
whereas the vomiting (emetic) type of illness is believed
expanded (Wu et al., 2016).
to be caused by a low-molecular-weight, heat-stable
peptide that has been named cereulide (Schoeni and
Wong, 2005). In humans, the diarrheal syndrome is TREATMENT
thought to be the consequence of a food-borne infection
with enterotoxic B. cereus following the observation It is important to remember three factors when a food-
that the diarrheal enterotoxins are produced during the borne problem is included in the differential diagnosis:
vegetative growth of B. cereus in the small intestine. the presenting clinical signs, the possible exposure to
B. cereus food poisoning has been classically associated foodstuffs not normally included in the animal’s diet, and
with fried rice and other cooked rice dishes because the the interval between exposure and onset of clinical pro-
bacteria is frequently present in uncooked rice and heat- blems. Some of these may not be known at the time of
resistant spores may survive cooking. If cooked rice is initial presentation but should be explored as the case is
subsequently held at room temperature, vegetative forms developed.
multiply, and a heat-stable toxin is produced that can In general, treatment of garbage intoxication in ani-
survive brief heating, such as stir frying. B. cereus food mals should be directed at correcting the fluid and elec-
poisoning can also be associated with meat- or trolyte abnormalities along with considerations of
vegetable-containing foods after cooking where the acid base balance. As mentioned previously, noncompli-
food was held above room temperature for a prolonged cated cases will often resolve within hours of presentation
period of time. Dogs have been shown to be susceptible with only supportive care. However, because the clinical
to B. cereus food poisoning (Chastain and Harris, 1974) signs can be similar to those of more serious conditions, a
with watery diarrhea reported as the most consistent more thorough diagnostic workup (e.g., survey abdominal
manifestation. radiographs) and close observation should always be