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Bacillus anthracis and Anthrax (page 1)
(This chapter has 5 pages)
© Kenneth Todar, PhD
The anthrax bacillus, Bacillus anthracis, was the
bacterium shown to be the cause of a disease. In 1877, Robert Koch grew
the organism in pure culture, demonstrated its ability to form
and produced experimental anthrax by injecting it into animals.
Figure 1. Robert Koch's original
photomicrographs of Bacillus anthracis, the agent of anthrax.
the cell morphology and spore position with the Gram stain below
(Figure 2). This is Bacillus anthracis. Beware of phony and
images of B. anthracis on the internet, including some that are
posted by otherwise credible websites. Look for large cells with square
ends and centrally-located ellipsoid spores when identifying Bacillus
Bacillus anthracis is
large, Gram-positive, sporeforming rod, 1 - 1.2µm in width x 3 -
5µm in length. The bacterium can be cultivated in ordinary
medium under aerobic or anaerobic conditions. Genotypically and
it is very similar to Bacillus cereus, which is found in soil
around the world, and to Bacillus thuringiensis, the pathogen
larvae of Lepidoptera. The three species have the same cellular
size and morphology and form oval spores located centrally in a
Figure 2. Bacillus
anthracis. Gram stain. 1500X. The cells have characteristic
ends. The endospores are ellipsoidal shaped and located centrally in
sporangium. The spores are highly refractile to light and resistant to
Bacillus thuringiensis is
distinguished from B. cereus or B. anthracis by its
for Lepidopteran insects (moths and caterpillars) and by production of
an intracellular parasporal crystal in association with spore
The bacteria and protein crystals are sold as "Bt" insecticide, which
used for the biological control of certain garden and crop pests.
Figure 3. Bacillus
Phase Photomicrograph of vegetative cells, intracellular spores (light)
and parasporal crystals (dark). 1000X.
Bacillus cereus is a
inhabitant of the soil, but it can be regularly isolated from foods
as grains and spices. B. cereus causes two types of
intoxications (as opposed to infections). One type is characterized by
nausea and vomiting and abdominal cramps and has an incubation period
1 to 6 hours. It resembles Staphylococcus aureus food poisoning
in its symptoms and incubation period. This is the "short-incubation"
emetic form of the disease. The second type is manifested primarily by
abdominal cramps and diarrhea with an incubation period of 8 to 16
Diarrhea may be a small volume or profuse and watery. This type is
to as the "long-incubation" or diarrheal form of the disease, and it
food poisoning caused by Clostridium perfringens. In
type, the illness usually lasts less than 24 hours after onset.
The short-incubation form is caused by a preformed, heat-stable emetic toxin, ETE. The mechanism
and site of
action of this toxin are unknown, although the small molecule forms ion
channels and holes in membranes. The long-incubation form of illness
mediated by the heat-labile diarrheagenic enterotoxin Nhe and/or hemolytic enterotoxin HBL, which
intestinal fluid secretion, probably by several mechanisms, including
pore formation and activation of adenylate cyclase enzymes.
Figure 4. Bacillus cereus.
stain. 450X. Bacilli are large bacteria, so that they are readily
with the microscope's "high dry objective" ........but you can't detect
anything about their spores. This could be a Lactobacillus.