Exam (elaborations)
USMLE STEP 1 Microbiology A Exam questions with answers
- Course
- Institution
USMLE STEP 1 Microbiology A Exam
[Show more]
Seller
Follow
DESTINYGRACE
Content preview
USMLE STEP 1 MicrobiologyWhat is a special cellular component of fungal membrane targeted in anti-fungal
medication? - answerErgosterol
A major sterol
What is the special component of bacterial cell wall? - answerPeptidoglycan
Where are the normal flora found? Contributions to health? Causes of infection? -
answerLocation:
- 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? - answerNo
Sterile environment
What is a medically important normal flora found in the nose? - answerStaphylococcus
aureus
What are the pathogenicity mechanisms? (8) - answer1. 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? - answer1. 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? - answer1. 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? - answer- 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)? -
answerkj: "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? -
answerMacrophages "block" in the microorganism forming *granulomas*
What is the type III secretion system? - answerAbility found in many pathogens
Capable of secreting toxins into host cell (macrophages) without entering it; tunnel
between bacteria to host cell
What are immune-mediated damage mechanisms? - answer- Cross-reaction of
bacteria-induced antibodies with tissue antigens (Rheumatic fever; type II
hypersensitivity)
- Delayed hypersensitivity and the granulomatous response (type IV hypersensitivity)
- Immune complexes (type III; poststrep acute glomerulonephritis)
- Peptidoglycan-*teichoic acid of G+ cells* (chemotactic neutrophils; structural toxin
released at cell death)
Infection: Physical damage mechanisms? - answerSwelling from infection
Large size of organism may cause blockage
, Ulcerations
What is LPS? G- or G+? - answerLipopolysaccharide = Endotoxin
- *Gram NEGATIVE* (part of outer membrane)
- Toxic portion is *lipid A* (generally released at cell death; *exception*: N. meningitidis;
over produces outer membrane fragments)
- LPS is heat stable; cannot be converted to toxoid
What is the endotoxin mechanism? - answer- LPS activates macrophages (release
TNF-⍺, IL-1, IL-6)
- Macrophages activation and products lead to tissue damage
- Damage to endothelium from bradykinin-induced vasodilation leads to shock
- Coagulation (DIC) is mediated through the activation of Hageman factor
What is the exotoxin? Mechanisms of action? - answerExotoxins: protein toxins
secreted by G+/G-
- can be produced into toxoids
- A-B ('two') component protein toxins
- A = active (toxic) component; ex: ADP-ribosyl transferase
- B = binds; binds to specific cell receptors to facilitate internalization
- Cytolysins: lyse cells from outside by damaging membrane
- C. perfringens alpha toxin is a lecithinase
- S. aureus alpha toxins insert itself to form pores in the membrane
What are some exotoxins subclasses? - answerEnterotoxins
Neurotoxins
Cytotoxins
What are some bacteria with cytolysin-function? - answerC. perfringens: alpha toxin is a
lecithinase; damages cell membranes; myonecrosis
S. aureus: alpha toxins form pores in membrane, becomes leaky
What are some exotoxins that inhibit protein synthesis? - answer"A VERy SHITty Dip"
A: exotoxin A
VER: Verotoxin
SHIT: Shiga-Toxin
Dip: Diphtheria toxin
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller DESTINYGRACE. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $15.49. You're not tied to anything after your purchase.
Can Stuvia be trusted?
4.6 stars on Google & Trustpilot (+1000 reviews)
77858 documents were sold in the last 30 days
Founded in 2010, the go-to place to buy study notes for 14 years now