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USMLE STEP 1 Microbiology Exam Prep Questions And Answers(202472025)
What is a special cellular component of fungal membrane targeted in anti-fungal
medication? - ✔✔Ergosterol
A major sterol
What is the special component of bacterial cell wall? - ✔✔Peptidoglycan
Where are the normal flora found? Contributions to health? Causes of infection? -
✔✔Location:
- found on body surfaces contiguous with outside environment (GI, etc.)
- Semipermanent (dependent on life-changes)
Contributions to health:
- Protective functions by maintaining a certain pH other microorganisms cannot
proliferate
- Nutritional: synthesizing vitamin K + B
Causes of infection:
- "Getting lost" (E. coli to urethra causing UTI)
- Overgrowth due to immunocompromised state
Are there normal flora in the blood or organs? - ✔✔No
Sterile environment
,What is a medically important normal flora found in the nose? - ✔✔Staphylococcus
aureus
What are the pathogenicity mechanisms? (8) - ✔✔1. Colonization (adherence)
2. Avoiding immediate destruction by host defense sys.
3. "Hunting + Gathering" needed nutrients
4. Antigenic variation
5. Ability to survive intracellularly
6. Type III secretion systems
7. Inflammation of Immune-mediated damage
8. Physical damage
What are the types of colonization? - ✔✔1. Adherence to cell surface
- *Pili*/fimbriae: primary mechanism in most G- bacteria (E. coli)
- Teichoic acids: G+ bacteria (acts as an antigenic determinant)
- Adhesins
- IgA proteases
2. Partial adherence
- biofilms (S. epidermidis, S. mutans)
(Biofilms are densely packed microorganisms forming a protective 'film' by doing
so; "cops standing outside of general admission; cannot get to people within general
admission area doing illegal things")
What are the types of mechanism used in avoiding immediate destruction by host
defense system? - ✔✔1. Anti-phagocytic surface components (inhibit
phagocytosis):
- *Capsules*/slim layers: "bar of soap slippery"
,kj: "Some Killers Have Pretty Nice Capsules Bro"
S: Streptococcus pneumoniae
K: Klebsiella penumoniae
H: Haemophilus influenzae type B
P: Pseudomonas aeruginosa
N: Neisseria meningitidis
C: Cryptococcus neoformans
B: Bordetella pertussis
- Streptococcus pyogenes: M protein
- Neisseria gonorrhoeae: Pili
- Staphylococcus aureus: A protein (binds IgG-Fc portion)
"MAP"
2. IgA proteases
3. Siderophores: steal (chelate) iron
What are antigenic variation mechanisms and microorganisms? - ✔✔- Changing
surface antigens to avoid immune destruction
- N. gonorrhoeae: pili + outer membrane proteins
- Trypanosoma brucei rhodesiense + T. b. gambiense: phase variation
- Enterobacteria: capsular and flagellar antigens may or may not be expressed
, What are bacteria with abilities to survive intracellularly (obligate/facultative)? -
✔✔kj: "Listen Sally Yer Friend Bruce Must Leave" (Facultative Intracellular bugs)
List: Listeria
Sal: Salmonella
Yer: Yersinia
Fr: Francisella
Bruce: Brucella
M: Mycobacterium tuberculosis
Le: Legionella
Obligate intracellular: "stay inside cells when its Really Chilly and Cold" (Can't
make own ATP)
R: Rickettsia
C: Chlamydia
C:Coxiella
1. Evading intracellular killing by professional phagocytic cells: allows intracellular
growth
- M. tuberculosis: inhibiting phagosome-lysosome fusion (slime layer)
- Listeria: escapes phagosome into the cytoplasm before phagosome-lysosome
fusion (rocket-shooting cell to cell)
2. Invasins: ability to invade non-phagocytic cells
- Yersinia pseudotuberculosis (causing diarrhea)
What happens when intracellular organisms escape macrophage phagocytosis? -
✔✔Macrophages "block" in the microorganism forming *granulomas*
What is the type III secretion system? - ✔✔Ability found in many pathogens
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