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USMLE Step 1 Microbiology B Exam questions and answers 100% accurate
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USMLE Step 1 Microbiology B Exam
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USMLE Step 1 MicrobiologyWhat's unique to the gram positive bacteria in terms of the cell wall? -
answerLipoteichoic acid (combination of lipids and teichoic acids)
What's unique to the gram negative bacteria in terms of the cell wall? - answer-
Endotoxin/LPS in the outer membrane
-Periplasm (space between the cytoplasmic membrane and the outer membrane)
What's the cell membrane/wall of Mycoplasma like? - answerIt has sterols and it doesn't
have a cell wall so it doesn't Gram stain
What's the cell membrane/wall of Mycobacteria like? - answerIt contains mycolic acid
and has a high lipid content
What specific things don't Gram stain well? - answer"These Microbes May Lack Real
Color"
Treponema (too thin to be visualized)
Mycobacteria
Mycoplasma (no cell wall)
Legionella pneumophila (intracellular)
Rickettsia (intracellular)
Chlamydia (intracellular and lacks muramic acid in cell wall)
What stain do you use for mycobacteria? - answerAcid fast stain
How do you visualize treponemes? - answerDark-field microscopy and fluorescent
antibody staining
How do you stain Legionella? - answerSilver stain
(Legionella is named for affecting old men with silver hair so you use silver stain)
What do you use the Giemsa stain for? - answer"Big Tits Really Call Peter" because
Giemsa sounds like a girl's name
Borrelia
Trypanosomes
Rickettsiae
, Chlamydia
Plasmodium
What do you use the PAS/Periodic Acid Schiff stain for? - answer"PASs the sugar"
stains glycogen, muccopolysaccharides
Used to diagnose Whipple disease (Tropheryma whipplei) bc Mr. Whipple puts sugar in
his coffee
What do you use the Ziehl-Neelsen (carbol fuschin) stain for? - answerAcid-fast
organisms: Nocardia and Mycobacteria
What do you use the India ink stain for? - answerCryptococcus neoformans because
cryptococcus sounds funny in an Indian accent
What do you use the silver stain for? - answerLegionella
Fungi like pneumocystis
H. pylori
What do you culture H. influenzae in? - answerChocolate agar with factors V (NAD+)
and X (hematin)
Because you want chocolate when you have the flu between the ages of 5 and 10
What do you culture N. gonorrhoeae and N. meningitidis in? - answerThayer Martin (or
VPN) media (Vancomycin inhibits gram positive organisms, Polymyxin inhibits gram-
negative organisms except Neisseria, and Nstatin inhibits fungi)
Because thayer martin has to live alone like Doc Martin
What do you culture B. pertusses in? - answerBordet-Gengou (potato) agar (Bordet for
Bordetella)
What do you culture D. diptheriae in? - answerTellurite agar, Loofler medium
What do you culture M. tuberculosis in? - answerLowenstein-Jensen agar
What do you culture M. pneumoniae in? - answerEaton agar, requires cholesterol
Because you get pneumonia from living in the Eton dorms where it's really cold and
rainy in England
What happens when you culture lactose-fermenting enterics on MacConkey agar? -
answerThey make pink colones because fermentation produces acidY
What do you culture E.coli in and what happens? - answerEosin-methylene blue (EMB)
agar --> colonies with a green metallic sheen
What do you culture Legionella on? - answerCharcoal yeast extract agar buffered with
cysteine and iron
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