The Genus Bacillus (page 5)
(This chapter has 6 pages)
© Kenneth Todar, PhD
Pathogens of Animals: Bacillus
and B. cereus are the predominant pathogens of medical
Paenibacillus alvei, B. megaterium, B. coagulans, Brevibacillus
B. subtilis, B. sphaericus, B. circulans, Brevibacillus brevis, B.
licheniformis, P. macerans, B. pumilus and B. thuringiensis
have been occasionally
from human infections.
B. anthracis is the causative agent of anthrax, and B.
cereus causes food poisoning. Nonanthrax Bacillus
can also cause a wide variety of other infections, and they are being
with increasing frequency as pathogens in humans.
Anthrax is primarily a disease of domesticated and wild animals,
herbivorous animals, such as cattle, sheep, horses, mules and goats.
become infected incidentally when brought into contact with diseased
which includes their flesh, bones, hides, hair and excrement. In the
States, the incidence of naturally-acquired anthrax is extremely rare
cases of cutaneous disease per year). Worldwide, the incidence is
although B. anthracis is present in most of the world's soils.
The most common form of the disease in humans is cutaneous
which is usually acquired via injured skin or mucous membranes. A minor
scratch or abrasion, usually on an exposed area of the face or neck or
arms, is inoculated by spores from the soil or a contaminated animal or
carcass. The spores germinate, vegetative cells multiply, and a
gelatinous edema develops at the site. This develops into papule within
12-36 hours after infection. The papule changes rapidly to a vesicle,
to a pustule (malignant pustule), and finally into a necrotic ulcer,
infection may disseminate, giving rise to septicemia. Lymphatic
also occurs within seven days. In severe cases, where the blood stream
is eventually invaded, the disease is frequently fatal.
Another form of the disease, inhalation anthrax (woolsorters'
disease), results most commonly from inhalation of spore-containing
where animal hair or hides are being handled. The disease begins
with high fever and chest pain. It progresses rapidly to a systemic
pathology and is often fatal if treatment cannot stop the invasive
of the infection.
Gastrointestinal anthrax is analogous to cutaneous anthrax
occurs on the intestinal mucosa. As in cutaneous anthrax, the organisms
probably invade the mucosa through a preexisting lesion. The bacteria
from the mucosal lesion to the lymphatic system. Intestinal anthrax
from the ingestion of poorly cooked meat from infected animals.
anthrax is rare but may occur as explosive outbreaks associated with
of infected animals.
The pathology of anthrax is mediated by two primary determinants of
bacterial virulence: presence of an antiphagoytic capsule, which
bacterial invasion, and production of a powerful lethal toxin, the
For more information on anthrax, including use and detection of Bacillus
anthracis as an agent of bioterrorism, please see the chapter on Bacillus
anthracis and Anthrax.
Bacillus anthracis Gram
Bacillus cereus food poisoning
Bacillus cereus causes two types of food-borne intoxications.
One type is characterized by nausea and vomiting and abdominal cramps
has an incubation period of 1 to 6 hours. It resembles
aureus food poisoning in its symptoms and incubation period. This
the "short-incubation" or emetic form of the disease. The
type is manifested primarily by abdominal cramps and diarrhea with an
period of 8 to 16 hours. Diarrhea may be a small volume or profuse and
watery. This type is referred to as the "long-incubation" or diarrheal
form of the disease, and it resembles more food poisoning caused by
perfringens. In either type, the illness usually lasts less than 24
hours after onset.
The short-incubation form of disease is caused by a preformed
enterotoxin. The mechanism and site of action of this toxin are
The long-incubation form of illness is mediated by a heat-labile
which apparently activates intestinal adenylate cyclase and causes
This bacterium is dealt with separately in the medical section of
text at Bacillus
cereus and Food Poisoning.
Colonies of Bacillus
(right) and Bacillus cereus (left) on a plate of blood agar.
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