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Corynebacterium Diphtheriae for the USMLE Step 1 | Physeo - USMLE Library | YouTubeToText
YouTube Transcript: Corynebacterium Diphtheriae for the USMLE Step 1
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welcome to section 8 of bacteria this is
our bacteria overview figure in this
video we'll be discussing
carinibacterium diphtheriae which you
can see right here quranibacterium
diphtheriae sounds kind of like corn so
we thought a haunted corn maze scene
would work well to help you remember
this organism as you can see from the
image this corn maze is getting shut
down but why by the end of the video it
will all make sense before we go any
further pay attention to the background
that's right there's a purple looking
sunset just like in our other videos
this should help you remember that
quranic bacterium diphtheriae is gram
positive this is an actual gram stain of
qurani bacterium diphtheriae notice that
the organism appears purple hence the
gram positive classification but it's
also rod shaped which is why it's a
bacillus the shape is a bit unique
because it looks kind of like a club you
can see this pretty obviously right here
notice that there's a prominent end on
the organism right here okay with this
in mind let's return to the story the
corn maze is being shut down because
this poor kid has lice all over his head
which he contracted while he was in the
corn maze his mother wasn't too happy
about this so she's on the phone
complaining about how this terrible
business needs to be shut down we've
shown lice on this kid's head because it
sounds kind of like lysogenic this part
of the scene should help you remember
that carinibacterium diphtheriae must
first be lysogenized by a bacteriophage
before it produces a virulent exotoxin
simply put this just means that a virus
which codes for the diphtheria exotoxin
must integrate its nucleic acid into the
bacterium's genome in order for the
bacterium to become dangerous so again
lys for lysogenized also notice that the
mom is extremely distressed about this
whole situation that's why she's using
her asthma inhaler to get more oxygen
and attempt to calm her down we've used
the inhaler in other videos to represent
aerobic organisms but let me refresh
your memory inhalers are commonly used
by asthmatics to facilitate oxygen
delivery to the lungs so it can be
thought of as a symbol for aerobic
organisms which are bugs that grow well
in the presence of a lot of oxygen so
the asthma inhaler in this image should
help you remember that crinobacterium
diphtheriae is an aerobic organism
finally notice that she's using her
telephone to tell the agency about how
her son got lice in this filthy corn
maze telephone and tell sound kind of
like telluride agar so these two ideas
should help you remember that the
organism can be grown on telluride agar
this is an image of cystine telluride
agar telluride is just a mineral that is
used in the agar notice that there are
black colonies that can be seen in the
image this is most apparent right here
okay moving on notice that we've added a
guy in an alien costume next to the corn
maze this shouldn't be too surprising
this is a haunted corn maze after all so
a scary looking alien guy seems pretty
fitting anyways we've included this
alien guy in the image to help you
remember that aniline dyes are used to
stain metachromatic granules red and the
rest of the cell blue metachromatic
granules are inclusions seen within the
organism that can be used during atp
synthesis so again alien for aniline
dyes if you look towards the back of the
image you can see that there is mist
near the corn maze we'll be using mist
to represent that an organism is
transmitted through aerosolized
respiratory droplets because mist
carries water molecules just like
respiratory droplets carry pathogens
okay now let's talk about the guy in the
booth notice that he's pulling on his
tie from all of the stress of his
business being shut down the tie wraps
around the neck and the fact that he's
pulling on it should help you remember
that karani bacterium diphtheriae causes
pharyngitis now you can see why he's so
stressed out this guy with a bureau
shirt on is handcuffing him must be a
pretty serious crime to have your
business infested with lice this part of
the scene should help you remember
details about the diphtheria toxin this
toxin has two subunits an a subunit and
a b subunit the letter b in bureau on
this guy's shirt is here to help you
remember that this part of the scene is
about the b subunit of the toxin the b
subunit binds to host cell receptors and
induces endocytosis of the toxin to help
you remember the function of the b
subunit we've shown the bureau guy
handcuffing the business owner just like
b subunit binds to the host cell this
bureau guy is binding the business owner
with handcuffs okay now let's discuss
the a subunit of the toxin to help you
remember this we've shown another guy in
a shirt that says agency the a in agency
should help you remember that this part
of the scene is about the a subunit the
a subunit inhibits host cell protein
synthesis by inhibiting elongation
factor 2 or ef2 during elongation of
protein synthesis to help you remember
this we've shown the agency guy using an
extendable baton to silence this group
of protesters so extendable baton for
inhibits elongation factor two also
notice that for your entertainment we've
shown this cowardly man running away
from the scary alien right here he
doesn't really mean anything
specifically but hopefully he'll help
you remember the alien in the image
which is ultimately here to help you
remember that aniline dyes are used to
stain metachromatic granules red and the
rest of the cell blue as we discussed
earlier now we've added some heat lamps
to the scene businesses commonly use
these outdoors to help keep their
customers warm so it seems pretty
fitting the heat lamps generate heat
just like someone with a fever generates
a lot of heat so we've included these to
help you remember that a fever may be
seen in infected patients next notice
that we've included some tires in the
background just like we did in our c
diff image the tires are circular and
resemble the cell membrane i guess you
could say they're kind of like a
membrane but not quite so
pseudomembranes these should help you
remember that a pseudo-membrane is
classically seen in the pharynx on
physical examination this is an image of
what the pseudomembrane looks like as
you can see it's a grayish white
substance that has adhered to the
posterior pharynx right here
okay now let's turn our attention to the
other agency guy in the back of the
scene who's closing off the corn maze
with a rope if you look closely at the
rope you can see that it looks kind of
like sausage links this resembles the
myelin sheath around an axon so we've
shown it in this image to help you
remember that crying bacterium
diphtheriae is neurotoxic all of these
agents didn't walk here they came here
in their car which you can see on the
left side of the image the car should
help you remember that the organism is
also cardiotoxic this may be manifested
as myocarditis heart block and
arrhythmias so car for cardiotoxic we've
also shown this elk in the background
who's looking for some food looks like
he's found a big field of corn that's
ready to be eaten elk sounds kind of
like elic so we've included it in this
image to help you remember that an elic
test can be used to identify toxogenic
from non-toxigenic strains of qurani
bacterium diphtheriae next notice that
this guy is laughing laughing sounds
like loffler's media so we've included
him to help you remember that carine
bacterium diphtheriae can be cultured in
lofler's medium where the metachromatic
granules may be seen more easily okay so
why was this guy laughing in the first
place as you can see he's not a fan of
the feds so he's laughing while his
friend pops the fed's tires if you look
closely you can see that this guy in the
green shirt is using a syringe to pop
the tires just like in other videos a
syringe is our symbol for a vaccine so
this part of the scene should help you
remember that there is a toxoid vaccine
which can prevent diphtheria you'll
often hear tdap or dtap which is a
combination of multiple vaccines and
this is how the vaccine is usually given
so again guy popping car tires with a
syringe for vaccine finally we've shown
the car suspended by little y-shaped
suspension tools that look kind of like
immunoglobulins this is to help you
remember that if an unimmunized
individual becomes infected then
pre-formed antibody can be administered
to help prevent systemic complications
okay now that we've covered the image
let's review with a question a 12 year
old boy who recently moved to the united
states from nepal is brought to the
emergency department due to fever
pharyngitis and heart palpitations his
temperature is 38.5 degrees celsius but
other vital signs are normal physical
examination is significant for a great
exudate on the posterior pharynx a swab
of the exudate is obtained on microscopy
there are gram-positive rods with
granules that stain deeply with aniline
dyes he is admitted to the hospital
which of the following should be done
immediately to prevent additional
complications a careful monitoring of
neurological status b intubation c
serial electrocardiograms
d pre-formed anti-toxin administration
or e vaccine administration okay
hopefully from the question stem you
notice that this boy's presentation is
consistent with chronic bacterium
diphtheriae a few points from the
question stem that are suggestive of
this diagnosis include a recent move
from nepal which suggests a lack of
immunization a great exudate on the
posterior pharynx and gram positive rods
with granules that stain deeply with
aniline dyes the exudate is describing
the pseudomembrane we talked about
earlier this is a pretty important point
questions on the actual step one test
we'll commonly avoid buzzwords like
pseudomembranes and instead we'll
describe the pseudomembrane so for
example a gray exudate on the posterior
pharynx okay with this in mind we're
asked what should be done immediately to
prevent additional complications the
correct answer is d pre-formed
anti-toxin administration the anti-toxin
contains neutralizing antibodies that
inactivate the diphtheria toxin however
the anti-toxin is only useful before
toxin enters the cell so it must be
administered immediately a is a good
idea and should eventually be done
because diphtheria is neurotoxic however
administration of pre-formed antitoxin
is more important because any delay may
allow more of the toxin to enter the
cells b is unnecessary at this point
because the boy's respiratory rate is
normal so he doesn't appear to be in any
respiratory distress however careful
airway management is important because
the pseudomembrane may cause airway
obstruction so b is incorrect c is also
a good idea because diphtheria is
cardiotoxic but just like a
administration of the antitoxin is more
important so c is incorrect e should
also be done but the immune response to
vaccination is slow therefore the
antitoxin should be given first in
someone who is acutely ill and then
vaccine administration can be given
later so e is also incorrect
from the image recall that the little y
shaped suspension tools under the car
that look kind of like immunoglobulins
represent the pre-formed antibody or
anti-toxin which should be administered
to prevent systemic complications in
acutely ill patients and with that we've
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