Corynebacterium diphtheria; a bacteria.
Corynebacterium are gram-positive bacillus which are aerobic
and non-sporm -
spore forming rods with meta-chromatic granules
which you can see if you focus closely on the slide with the
In addition, the organisms appear club shaped, you can see a
prominent end of each end of the bacillus.
If grown on Löffler medium, they appear as gray to black
colonies on the Tellurite agar.
Now, why is Löffler medium important?
Because Dr. Loeffler was one of the discoverers of
Corynebacterium are transmitted by aerosol droplets,
they are very typically present in the respiratory flora
and it does not take much for them to be sneezed or coughed.
Also, if there's a break in the skin with somebody who has a
cutaneous infection with diphtheria,
it can be transmitted in that way as well.
There are several important clinical diseases associated
The first is the classic or the respiratory diphtheria which
causes a pseudomembranous pharyngitis.
Pseudomembrane; this is not a true membrane or tissue which
is found in the pharynx
but it is created by all of the necrotic and inflammatory
debris which coats the inner part of the pharynx.
Many times, it also covers and crosses or blocks the
So patients with true respiratory diphtheria,
due to the pseudo-membrane are unable to breathe because
their trachea is completely blocked by that mechanism.
In addition, they may have severe lymphadenopathy which you
see in the picture on the lower right.
The patient has what looks like a bull neck that is really a
reference to a very swollen neck
due to very significantly swollen lymph nodes in the
anterior and the posterior cervical chains.
The other form of diphtheria though is wound or cutaneous
And this starts initially in a very minor fashion as a small
papule; a small red bump,
which then develops into the picture you see in the upper
right as a chronic nonhealing ulcer.
Rarely, both of these illnesses can present and progress to
a systemic toxemia
in which the patients develop multiorgan disease or damage
to distant organs
including the myocardium causing cardiac failure,
and then renal tubular necrosis causing kidney failure.
Pathogenesis. How does this illness - or how does this
organism cause illness?
It starts in the form of a bacteriophage, a lofty little
which introduces itself into the DNA of the organism and
that encodes a diphtheria exotoxin.
The toxin is really the major cause of the disease in
because it ribosylates ADP present in the elongation factor.
That doesn't sound too awfully bad until you realize that
and especially elongation factor 2 is critical for the
elongation of protein chains.
So if you inhibit its function as happens with diphtheria
the patient's cells are unable to protein synthesize.
They're unable to do the normal works of life.
And so that causes cell death and the secondary clinical
How do we make the diagnosis?
Well, a clinical diagnosis is probably the most likely one,
but you'll be - also expected to know how this might be done
in the laboratory.
Now let's discuss the lab diagnosis,
definitive diagnosis of the theory that
requires a culture of corynebacterium
diphtheriae from respiratory tract secretions
or cutaneous lesions, as well as a positive
The presumptive diagnosis can be made with a
gram stain that shows gram positive rods
typically appearing as club shaped rods in a
zigzag period, or what may be
described as a Chinese character
For testing purposes, remember, you may also
see monochromatic granules when staining with
aniline dyes or lafleur's media.
Further confirmation can be
ascertained by additional
testing for exam purposes.
Remembering this organism is catalase.
Positive is the most important.
There are several methods to test for the
diphtheria toxin, including a rapid test and
a PCR test that identifies the gene.
It should be noted, however, that a negative
PCR test is very sensitive at
excluding a diphtheria diagnosis.
Now, instead of delaying treatment while
awaiting these testing results, a high
clinical suspicion is important and is all
that is required to begin.
Administration of the anti toxin.
Do not wait.
Finally, any cases of clinical
disease caused by
corynebacterium diphtheria toxin must be
reported to your local and
regional health department.
A positive laboratory test without clinical
symptoms can be considered only to be a
carrier infection, which does not require
So, what about that prevention?
Well, diphtheria has been a component of the diphtheria
pertussis toxin vaccine for a very long time
and it is very successful, but a booster is necessary.
If a patient however is not protected; does not have that
immuno protection from vaccine
and they developed disease related to diphtheria.
Then tetanus and diphtheria immunoglobulin can be used to
neutralize the toxins of the actual disease.
So in treating a patient with diphtheria, penicillin is the
typical antibiotic which is most successful.
However, erythromycin also works for those who are
We would also however use antibiotics to treat close
contacts of the index patient
because they may have acquired disease via that respiratory
or cutaneous mechanism.
So diphtheria, hopefully is a very rare infection to
but it is an important organism to remember and to
Again, keeping in mind that it looks like metachromatic
clubs under the microscope
and that it can cause a pseudomembrane in the airway of a
patient who has respiratory diphtheria.