Bacteroides, a bacteria.
The Bacteroides are gram-negative, anaerobic, and
and you can see them on the image projected on the slide.
These are pleomorphic organisms, again, because they have a
somewhat variable staining,
a pattern when they’re looked at on the gram stain.
In addition, they produce very foul-smelling short-chain
which is one of the signature presentations of a anaerobic
infection such as with Bacteroides.
They have broad antibiotic resistance as we’ll talk about
later in this presentation,
only a few antibiotics are known to have reliable efficacy
against the Bacteroides.
They do have weak endotoxin activity which contributes to
and unfortunately, they are known to be the normal flora of
many parts of the body.
Respiratory tract, gastrointestinal tract, and the genital
However, if one were to look at the most common location for
the Bacteroides bacteria, it is in the GI tract.
Think below the diaphragm for presence of Bacteroides.
The most clinically significant Bacteroides is Bacteroides
fragilis and this again,
below the diaphragm, an anaerobic cause of gastrointestinal
The pathogenesis of Bacteroides starts with its capsule in
so it is able to allow phagocytosis without death.
Then, therefore, the Bacteroides combined to peritoneal
surfaces after they leave their normal site
within the intestines at once binding to peritoneal surfaces
can create abscess formation.
The abscess formation in part is due to the human immune
system’s attempt to phagocytose unsuccessfully,
the organism itself and then, leading to innocent bystander
damage to the surrounding normal cellular tissue.
Surgery and trauma only accentuate the problem because they
can disrupt the abscess itself,
allowing the organism to then enter the bloodstream and/or
lymph structures and disseminate freely.
As the dissemination occurs, as the Bacteroides is now
getting free access to the rest of the body,
it releases further enzymes which can cause tissue
So, basically, a very significant enteric pathogen that is
until you disturb its normal habitat via surgery or via
The infections caused when that happens are typically
multiple intraabdominal infections with abscess formation.
Those can extend into the pelvis to cause abscesses or
suppurative pelvic infections
and as they disseminate causing entrance into the
a bacteremia or a septicemia. In some cases where the
intraabdominal infections and abscesses are extensive,
they can cause a reactive pleural effusion, so, an effusion
within the lung cavity between the lungs,
the pleura, and the chest cavity, and that effusion because
it is proteinaceous can become secondarily infected.
So, one can see infections extending from the abdomen to
above the diaphragm to cause pleural pulmonary infections.
Prevention and treatment, well, if one knows that one is
going in to do an intraabdominal surgical procedure,
in fact, many surgical procedures, there is known violation
of normal tissue boundaries of skin integrity,
the normal defense mechanisms which the human body has
and if one knows especially that intraabdominal surgery’s
going to occur
and has the potential to open up intestinal contents,
then, prophylactic antibiotics are indicated, specifically,
targeting the bacteria which normally live in the gut.
Once though an infection has become established, then,
removal, surgical removal of necrotic material,
purulent material, drainage of abscesses is critically
because antibiotics by themselves will be relatively
not effective in treating bacteria in the middle of an
abscess. Why might this be?
Several reasons, number one, antibiotics don’t have a
delivery mechanism to the inside of an abscess cavity.
There’s no blood supply to deliver them into the abscess.
Thus, they would have to diffuse in through a concentration
gradient which is a slow and completely unreliable process.
Second though is that within the abscess material itself is
a very low pH, a very acidic environment.
Almost all antibiotics are designed or naturally acquired to
function at normal pH of the body.
So, they don’t work well. The molecular structure
disintegrates at too high or too low a pH.
Thus, even if you could get an antibiotic delivered into an
abscess cavity, if it has a low pH,
that antibiotic will not be highly effective.
So, surgical drainage, surgical removal is critical, is
to actually treat those infections caused by Bacteroides
After the surgical drainage occurs, then, antibiotics using
especially metronidazole is the best approach.
Metronidazole is an antibiotic with excellent anaerobic
capabilities and excellent tissue penetration.
There are many available antibiotic regimens
that can be selected based on a patient's
medication tolerance, drug adverse effects,
or even suspicion for antibiotic
resistance in their organism.
Once the culture and susceptibility tests
are completed, then of course, the
antibiotics can be adjusted to better target
or focus on the patient's known infection.
One typical combination might be
metronidazole and cephalosporin.
Although single agent drugs such as
Chippenham or Chippenham sell acetate and
also would work.