Pseudomonas Aeruginosa, a bacteria.
Pseudomonas are gram-negative aerobic rods.
They have sometimes up to three flagella and they are
So when you hear them described in a case vignette,
you will frequently hear this organism is a non-fermenting,
gram negative rod.
They will likely not mention the flagella.
The organisms are oxidase and nitrate reduction test
and this is important, they have a very characteristic grape
fruity odor -
some likened this very much to grape chewing gum or grape
but it’s quite a prominent scent which actually is somewhat
Also, on culture, they appear greenish or blue greenish
due to production of a pyocyanin, a pigment which appears
blue or green.
Transmission. Pseudomonas are important especially in
hospital acquired infections
because they are ubiquitous throughout the environment
and especially in any reservoir that have some degree of
You might think of dialysis equipment, a respiratory
but also so too the sinks, the soap dispensers in the
hospital setting or even at home.
Whenever and wherever the moisture accumulates then
infection too can develop,
so it’s a difficulty for infection preventionists to
Let's look at some of the mechanisms of pathogenesis for
The first has to do with the pili or the attachment points.
These create a very strict adherence to respiratory
In addition, the antiphagocytic capsule is present which
also binds very strongly to tracheal epithelium.
So those two combine start the process known as biofilm
where the organism can start to coat the airway linings and
build upon itself.
Exotoxin A, typically is released as well, and this
ribosylates, adenosine diphosphate,
which is in the elongation factor known in cellular
If one inhibits the process of the elongation factor by
then protein synthesis and chain elongation cannot occur.
This is one of the principle mechanisms by which Pseudomonas
aeruginosa can cause disease.
But in addition, Pseudomonas in a way is smart.
Once one gets more than a couple of the Pseudomonas
organisms or bacteria together,
they start to sense the presence of other Pseudomonas in the
region and they communicate in a way,
no they're not using radio signals or something like that,
but there's definite proof that a group of Pseudomonas when
can start to navigate further biofilm production, further
growth, and then uniform production of the exotoxins.
In addition, exotoxins also exists which as the biofilm is
being put down,
can prevent phagocytic killing.
And then there are degradative enzymes which do the specific
damage to host tissues,
so in a way, Pseudomonas, while being ubiquitous in the
hospital setting, and water loving areas,
is also quite a nasty challenge because it can create this
which has many weapons to cause disease among host tissues.
So what are some of the infections seen with Pseudomonas?
Well, there are many.
The first and perhaps the most common are the urinary tract
especially in patients who have an indwelling catheter.
Why? Because Pseudomonas loves plastic and it loves the
micro areas protection
which are induced by having an indwelling catheter in the
urinary collecting system.
So, patient’s with foley or catheter associated urinary
are most likely to be growing pseudomonas aeruginosa.
Then there are the patients suffering with burn and wound
Again, because the diseased tissues have limited
immunosurveillance and they retain moisture,
it is possible for Pseudomonas to evade immunologic
detection and create further damage
in the burn tissue secondarily followed by entrance into the
blood system causing bacteremia and sepsis.
A very common source in which one sees Pseudomonas are the
otitis externa or swimmers ear infections.
Now, these maybe benign but talk to any child and perhaps
who suffered from this and it does not feel good.
Painful Pseudomona’s discharge from the external canal of
again, due to retention of moisture in that environment.
Sometimes, that otitis external can get out of control
something known as malignant external otitis or put the
other way around, malignant otitis externa.
This is sort of a swimmer’s ear gone really bad in which
there’s extensive pain
and then swelling and a very purulent discharge from the
external auditory canal.
If not recognized and not treated that infection can then
going into the central nervous system causing cranial nerve
damage, bacteremia and sepsis.
In fact, many times, malignant external otitis is mistaken
which is a different set of infection and a different type
of bacteria but they look somewhat similar.
The earlobe itself, the pinna protrude and are red, and very
and the patients are many times quite sick.
Skin infections. Ecthyma gangrenosum, roles trippingly off
but in itself is not a good process at all.
Ecthyma gangrenosum is typically caused by presence of
in the capillary beds of an infected tissue
creating an immunologic reaction which is uncontrolled.
And so, one will frequently see ecthyma gangrenosum in
patients who have a hematologic malignancy
especially those with leukemia or lymphoma
who are also neutropenic to the chemotherapy or about to
The lesions themselves are very focal, they look almost like
a gangrene so blackened, ischemic lesions
which start off as purpuric or hemorrhagic lesions and then
progress to superficial necrosis.
Folliculitis, this is also sometimes knows as hot tub
folliculitis and again it makes sense
because one has warm moist water retention in the areas of
the hair follicles
even after getting out of the hot tub
and precipitates a local infectious cellulitis at those
follicle roots, so most often,
as you see in the areas of the apocrine sweat glands but
also around the nipple, areola, arm pits -- you name it.
Typical treatment with that is going to be topical and it
would take sure time just waiting for it to resolve.
And then pulmonary infections.
These are perhaps the most commonly encountered in patients
who have an otherwise underlying chronic pulmonary process
such as those with cystic fibrosis
or chronic obstructive pulmonary disease, COPD.
These patients will typical have diffuse or bilateral
and it again comes from contamination of the airway with the
from other respiratory therapy equipment.
Keratitis. Now looking toward the eye and this can be a
fulminating process so typically patients will present
with some ulceration or some injury of the cornea
which then is secondarily infected by the pseudomonas.
If it starts and ends simply at the cornea, it may only be a
but the potential for this to extend to infect the entire
eye, a panophthalmitis, is quite extensive.
Disseminated infections. Typically coming from a point or a
focal source such as the lungs or perhaps ecthyma
as we talked about in leukemia patients,
but any patient with altered immunity is at risk to develop
And then osteomyelitis or perhaps more accurately called
This typically and classically is associated with a
such as a thorn or a nail or screw going through the sole of
and typically, an athletic shoe which is warm and moist and
sometimes stinky inside
and then penetrating and inoculating the sole of the foot
and the underlying cartilage in this bone structures with
Treatment. All these very significant infectious processes
while differing in severity,
all can respond to systemic treatment and the most common
start for antibiotic treatment
is with an antipseudomonal beta lactam penicillin or a
depending on the susceptibility of the isolate.
Now, Pseudomonas like increasingly other gram-negative
is acquiring more and more robust mechanisms of antibiotic
and so commonly, in those chronically ill patients,
one will see a need for even more evolved and more
aggressive antibiotic therapy
but as a proper starting point, starting with the
antipseudomonal beta lactam antibiotic or penicillin is
In some cases, double covering the treatment,
adding two antibiotics to more rapidly or more perhaps
aggressively reduce the organism load is appropriate.
The typical antibiotic to add to the antipseudomonal beta
lactam is an aminoglycoside,
something like a tobramycin or a gentamycin;
but the fluoroquinolones such as ciprofloxacin and others in
that family will also be effective.
So, as we look at the presence of Pseudomonas all around us,
keep in mind that it again, is a water loving green
culturing fruity grape juice smelling organism
which has a potential to do nothing more than a swimmers ear
or a hot tub folliculitis
but has the potential to cause incredibly extensive
Just say no to Pseudomonas.