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Streptococcus Pneumoniae for the USMLE Step 1

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welcome to section 10 of bacteria in

this section we'll be discussing the

streptococcus pneumoniae which you can

see on our overview figure right here

this scene takes place in the autumn

season and the characters you'll see

here are shown harvesting the crops and

cleaning up the mess so it's kind of

like a fall harvest scene the lawnmower

in the scene was just purchased in order

to make the fall harvest and cleanup

easier new mower sounds like pneumonia

so the new mower represents

streptococcus pneumoniae you see the

news tag on this brand new mower this is

to help you remember that it's a new

mower so new mower strep pneumoniae

notice anything else about the mower

that's right it's an incredibly ugly

purple color this is to help you

remember that strep pneumonia is a gram

positive organism so just like in other videos

videos

the purple represents gram positive this

is a Gram stain of streptococcus I first

off notice that the organism stains

purple which is why it's a gram positive

organism and second notice that the

bacteria are circular or Cox I shaped

and that they form long continuous

chains so the morphology we see here is

unique to streptococcus I now we've

added some alfalfa to the scene this is

to help you remember that streptococcus

pneumoniae is alpha hemolytic so alfalfa

for alpha hemolytic this is a figure of

the three types of hemolysis which we

discussed in more detail in section 7

which was our video on Listeria again

alpha hemolysis looks like this notice

the green appearing zone of partial

hemolysis surrounding the colony okay

let's return to the image notice that

now we've added this silly-looking chin

here Oh guy who's riding the mower he's

a bit sensitive about his chin so

throughout his life he's had to

overcompensate for this by exercising as

you can tell by his humongous muscles

the fact that he has a massive looking

chin and is sensitive about it

should help you remember that strep

pneumonia is opt ocean sensitive so

sensitive chin man for opt ocean

sensitive we discussed this figure in

section 9 which is our video on the

viridans group streptococci but recall

that if there is clearing around a disc

saturated with opt ocean then the

organism is up toshin sensitive notice

that there is a large zone of clearing

directly adjacent to this disc so if

this were an opt ocean disc then the

organism here would be opt ocean

sensitive for step one you need to know

that streptococcus pneumoniae is up

Oshin sensitive next notice that we've

added some interesting-looking Lance's

and tridents on the mower this is why

the opt ocean man purchased the new

mower in the first place he needed some

sharp new blades to help him with the

fall harvest it appears that these

gadgets are working well at cutting down

the alfalfa let's talk about the Lance's

first the Lance's on the back of the

mower have been included in this image

to help you remember that Streptococcus pneumoniae

pneumoniae

has a Lancet shaped diplococci

appearance under the microscope so

Lance's four Lancet shaped the Trident

seen on the front of the mower are our

symbol for the drug ceftriaxone the word

ceftriaxone has the sound tri in it so a

trident seems fitting likewise it has

the word ax in it so we'll be using

Trident sand axes to represent

ceftriaxone ceftriaxone is one of the

drugs commonly used to treat

streptococcus pneumonia we've also added

this scarecrow in the field which

appears to be doing a poor job scaring

away the birds the Scarecrow is our

symbol for macrolides

crow sounds like macro so a scarecrow

seems fitting for this class of drugs

just like ceftriaxone macrolides are

also commonly used to treat

streptococcus pneumonia so in summary

the treatment for strep pneumonia is a

macrolide in combination with

ceftriaxone as I mentioned a second ago

the scarecrow is doing a poor job at

scaring away birds as you can tell by

the quails sitting on his arm these

quails were included in the image to

help you remember the quelling reaction

this is a reaction in which antibodies

bind to the capsule of streptococcus

pneumoniae and it can be helpful in cero

typing the capsule over 90 strains of

strep pneumoniae have been discovered

and they're distinguished based on

differences in the polysaccharide

capsule therefore this reaction can

provide useful information about the

capsule so again

quails for quelling reaction this is an

image of the quelling reaction when anti

capsular antibodies and methylene blue

dye are used to stain the capsule it

swells and appears as a blue halo as you

can see in the image right here speaking

of a polysaccharide capsule look at

these sacs of apples we just added to

the back of the scene in our images a

sac is our symbol for a polysaccharide

capsule sac sounds like polysaccharide

so these sacs back here should help you

remember that strep pneumonia has a

polysaccharide capsule all of the apples

are back here because they've been

harvested to make apple juice the big

container next to the sack is full of

apples which is a

to be made into some delicious juice

we've also added a syringe on the sack

to help you remember that the vaccine

against strep pneumonia is directed

against the polysaccharide capsule we've

used syringes in other videos as our

symbol for vaccination and will continue

to use this throughout our image

mnemonic videos in the United States

there are two pneumococcal vaccines

including the 23 serotypes Exene and the

13 serotypes Exene these vaccines are

used to prevent disease in children

individuals who may be immunocompromised

and adults who are 65 years and older so

syringe on the sack for vaccine is

directed against the polysaccharide

capsule unfortunately some of the apple

juice has spilled on the ground

it's a tragedy so sad if you're weird

like my co-founder Rhett and you happen

to hate apples then maybe you're feeling

a bit relieved right now anyways this

bill green juice on the ground here is

our symbol for bile if you look closely

you can see ice cubes that have melted

in the center of the spill the melted

ice cubes inside of the green juice is

our symbol for bile soluble this makes

sense right the ice cubes are melting or

are soluble within the apple juice so

for step one you need to know that strep

pneumonia is bile soluble we covered

this test in more detail in section nine

so we're not going to discuss it again

this guy back here saw the mess so he

grabbed a mop and started cleaning it up

mops is a popular mnemonic that is used

to remember that strep pneumonia is the

most common cause of meningitis and

adults of all ages of tightest media and

children community acquired pneumonia

and sinusitis

in adults so mop for the mops mnemonic

this is an autoscopic image of acute

otitis media

notice that the tympanic membrane is

bulging out towards us and appears red

this is a classic physical exam finding

of otitis media we've also included this

guy towards the front of the image who's

helping cut down the vegetation here

notice that he's using a sickle this

seems pretty fitting with the story

considering that this is a fall harvest

scene right the sickle here is to help

you remember that strep pneumonia can

cause sepsis in patients with sickle

cell disease this is because sickle cell

patients are prone to becoming a splenic

and the spleen normally helps clear

encapsulated organisms therefore an a

splenic patient is at an increased risk

of developing severe infections from

encapsulated organisms

such as strep pneumoniae so sickle for

sepsis in sickle cell disease and a

splenic patients finally notice that

this guy is holding up a big pair of

scissors kind of like yard clippers

scissors are our symbol for proteases

and this should be fairly intuitive

protease azar enzymes that cleave

proteins just like scissors cleave paper

therefore the yard Clippers in this

image are here to help you remember that

strep pneumoniae produces an IgA

protease this is a virulence factor that

cleaves IgA and allows the organism to

evade the hosts immune response and

colonize the mucous membranes so

scissors for IgA protease okay let's

wrap up this section with a question a

67 year old female presents to the

emergency department due to sudden onset

nausea vomiting and confusion physical

examination is significant for a fever

of thirty eight point six nuclear

rigidity and altered Mental Status

empiric treatment is started and a

lumbar puncture is performed CSF Gram

stain reveals gram positive Lancet

shaped diplococci administration of a

vaccine directed against what bacterial

structure may have been helpful in

preventing infection hopefully from the

question stem you notice that this

patient has developed meningitis common

clinical features of meningitis include

a fever nuchal rigidity and altered

Mental Status strep pneumonia is the

most common cause of bacterial

meningitis and adults so this should

immediately be at the top of your

differential without any other information

information

however the question stem further states

that a CSF Gram stain reveals gram

positive Lancet shaped diplococci

therefore we can be confident that the

microorganism being described in the

question stem is strep pneumoniae with

this in mind we're asked what bacterial

structure the vaccine targets so the

answer is the polysaccharide capsule

from the image recall that the SAC back

here with the syringe on it is to help

you remember that the vaccine is

directed against the polysaccharide

capsule and with that we've concluded

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YouTube Transcript:
Streptococcus Pneumoniae for the USMLE Step 1