Bacillus, a bacteria. Bacillus are gram-positive rods that
are aerobic and are spore-forming.
Now, this is important because as we'll see,
most of the pathogenesis from the Bacillus species comes
from those spores and they get everywhere.
Importantly, Bacillus is one of the bacterium,
in fact, the only one with a completely polypeptide capsule.
This is important in protecting it from the attack of the
human immune system.
Now, we talk about or recognize two medically important
The first is Bacillus anthracis, the cause of anthrax. Most
cases of anthrax are cutaneous,
skin-associated, and they're inoculated by a vector, a fly.
However, Bacillus anthracis is one of the few organisms that
has been weaponized as a cause of bioterrorism
and we'll talk briefly about that as well. Bacillus cereus
is the other important species.
It is commonly referred to as B cereus as it is a cause of
very significant emesis,
vomiting disease related to spores created in rice.
When anybody has had that particular infection, it is no
hence, B cereus is a common microbiology joke.
Let's talk first about pathogenesis and we'll focus on
Bacillus anthracis contains two toxins important for its
and they're introduced by a third factor which allows the
toxins to be introduced.
The first toxin is edema factor and this is important for
modifying AMP within the target cell, creating it into a
The presence of cyclic AMP increases the presenting factor
or fluid leaking from the cell due to protein synthesis
The second factor, the lethal factor, cleaves phosphokinase
which also is important in cellular machinery and protein
The combination of these two lethal and edema factors is
very important in killing the target cell.
However, they require the presence of the third toxin or the
which creates a cluster of seven different protein factors
at the cell's surface,
in an effect, creating a porin or a channel through which
the edema and the lethal factor introduce.
Again, as noted, the capsule of Bacillus anthracis is
so, the combination of all these together leads to the
diseases caused by Bacillus anthracis.
What happens with the spores? How does one get infected with
As you see at the top of the slide, there is a biting fly
which seems to be central to cases of anthrax
and in most parts of the world, this is true.
The fly infects itself with spores coming from decompensated
waste or stool from bovine sources,
other infected animals, and then, can bite and introduce
anthracis spores into anybody including the human being.
However, the spores exist in vegetable material and
decomposition all over the world,
typically, sporulating in the presence of heat or humidity
and then, they can be ingested or inhaled, or even stepped
upon and ejected that way.
A very famous source of anthrax came from a person living in
New York City who purchased tribal drums from Africa.
Unfortunately, there were spores present in the hide
which had been used as the drum head and as soon as this
person in New York started beating the head of that drum,
he inhaled anthrax spores and acquired inhalational anthrax.
Note to self, don't buy drums from tribal Africa.
Now, let's talk about pathogenesis of Bacillus cereus or B
In this case, the cyclic AMP is increased within
enterocytes, the small cells lining the gut.
In addition to causing edema via that factor, they are a
which is associated with rapid onset of vomiting and a
heat-labile enterotoxin which when present,
is associated with onset of non-bloody diarrhea and
Of the three, the cyclic AMP is present almost all cases
and the heat stable enterotoxin is present almost all the
cases as well.
B cereus is primarily a very unpleasant hyperemesis disease.
Now, let's compare the two organisms and their diseases side
Here, if you look at the habitat for Bacillus anthracis and
we see that the spores are ubiquitous almost anywhere.
For Bacillus anthracis as noted before, the spores exist in
but also, in animal sources and those horrible drum heads in
Bacillus cereus is found also in the soil but also, it can
be transmitted into food sources.
The frequent exposure in this case is undercooked rice,
especially with Asian themed dishes and in cases where the
rice has been left to stew for a while.
Transmission, Bacillus anthracis, it's typically
whether it's inhalation of the spores as we noted or
ingesting of the spores themselves.
Occasionally, the spores are introduced through the bite of
a biting fly.
For Bacillus cereus as noted, the reheated rice syndrome is
and it is a frequent contamination of reheated foods. How to
identify the organisms?
Again, Bacillus are gram-positive rods and they're
but in Bacillus anthracis under the microscope, the spores
and the organisms are non-motile, they don't move. However,
Bacillus cereus are motile.
You can see them wiggle under the microscope.
Both organisms are aerobic, requiring oxygen.
Further, for Bacillus anthracis, when looking at it in
culture growth on blood agar,
it appears to grow in medusa-head colonies, little snakelike
forms of the organisms clustered together.
With Bacillus anthracis, the toxins are the exotoxin present
in that capsule which inhibits phagocytosis.
The protective factor which again clusters at the cell's
to allow injection or introduction through a porin of the
edema factor and the lethal factor.
Those last two factors together have to do with inhibiting
cell function, protein synthesis,
and creating edema and death of the cell.
For Bacillus cereus, there are two toxins, the heat stable
which creates vomiting and the heat-labile exotoxin which
creates that secretory diarrhea.
Both toxins may be present, although most commonly, it is
the heat-stable exotoxin with the vomiting.
How does one typically develop disease with these two?
Bacillus anthracis, the most common form of disease is
cutaneous anthrax as mentioned before.
This could be inoculated through the bite of the fly or
through some other pointed object.
Typically, patients with anthrax will develop a small papule
which may be somewhat pruritic
but it rapidly develops over several days into a deep ulcer
which has vesicles, lots of edema or swelling,
and then, secondary necrosis, septicemia, and frequently
The necrotic ulcer that develops in cutaneous anthrax
with a painless black center known as eschar.
The ulcer heals within 3-4 weeks and leaves
hyperpigmentation or scarring.
Pulmonary anthrax is due to inhalation of the spores
and it starts as a viral-like illness progressing rapidly to
respiratory failure and there's a high mortality.
If you recall from the short days of anthrax as a
patients were inhaling the spores delivered through the mail
and they were developing rapid onset of respiratory failure
and some deaths.
Bacillus cereus is notable for as a source of food
poisoning, very unpleasant food poisoning.
Rapid onset within 1-5 hours of ingestion so the patients
frequently know exactly
where they got the food poisoning from, and the restaurant
and the dish.
Patients such as those will have initial onset of nausea,
followed by hyperemesis,
the vomiting, and then severe abdominal cramps.
Some of those patients may go on to develop a watery or a
and again, the cramps are present.
Because that is a heat stable toxin, it takes 10-15 hours of
What do we do? How to prevent either organism from causing
In the case of Bacillus anthracis, we can vaccinate animals.
We certainly can create proper disposal of infected animals
and there is a vaccine for patients who are at risks.
You see them listed on this slide: fur and wool handlers,
physicians or healthcare providers responding to areas which
may be endemic for anthrax.
Treatment of anthracis is amoxicillin or penicillin if the
organism is sensitive.
However, we frequently don't have time to realize or
discover the susceptibility pattern
so most often, patients will start with ciprofloxacin or
secondarily, a tetracycline such as doxycycline.
Again, you may recall during the anthrax scares in the
there was a run on the drug ciprofloxacin and people were
going across the border to Mexico
to pick up stores of the antibiotic without a prescription.
Bacillus cereus, prevention is typically through
refrigerating the foods
after cooking or avoiding re-cooked rice if at all possible.
Also, if your friends tell you they acquired really bad
vomiting from a certain restaurant,
you may wish to go some place else.
If, however, one fails to heed that excellent advice and
develops hyperemesis vomiting disease,
then supportive therapy is your friend.
Replenishing the fluids, replenishing the electrolytes.
So, that wraps up what we know about Bacillus.
Again, two major forms: anthracis and cereus.
One, very serious, but not the cereus one.
The other is serious but not all that bad if you can support