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USMLE STEP 1 > Micro Basic > Flashcards

Micro Basic Flashcards

1
Q

Peptidoglycans
Composition
Function

A

Sugar backbone with peptide side chains cross linked by transpeptidase
Support. Protects against osmotic pressure

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2
Q

Lipoteichoic acid
Where is it?
What does it do?

A

Cell wall of Gram+

Induces TNF and IL1

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3
Q 
LPS
AKA
Location
What is it?
Components
A 
Endotoxin 
Outer membrane of Gram-
Major Surface Ag
Lipid A (induces TNF and IL1)
O polysaccharide is the antigen
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4
Q

Periplasm
What is it?
What kind of organisms
What does it contain

A

Space between cytoplasmic membrane outer membrane
Gram-
Hydrolytic enzymes include β lactamase

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5
Q

Capsule
Made from…
Function

A

Polysaccharides (except in Bacillus anthracis which contains D-glutamate)
Protects against phagocytosis

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6
Q

Pilus/Fimbria
Composition
Function

A

Glycoprotein

Mediates adherence of bacteria to cell surface. Sex pilus for conjugation

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7
Q

Flagellum
Composition
Function

A

Protein

Motility

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8
Q

Spore
Composition
Function

A

Keratin-like coat, Dipicolinic acid, Peptidoglycan

Resistance to heat, chemicals, dehydration

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9
Q

Glycocalyx
Composition
Function

A

Polysaccharide

Mediates adherence to surfaces (especially foreign surfaces)

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10
Q

Outer layer composition in Gram+ vs Gram- bacteria

A

+
Inside to outside:
Cytoplasmic membrane, Peptidoglycan (cell wall), Capsule
Pilus, Flagellum, Lipoteichoic acid (lipids + teichoic acids)
-:
Cytoplasmic membrane, Perplasm, Peptidoglycan, Endotoxin (LPS), Capsule
Pilus, Flagellum

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11
Q

Outer layers of Mycoplasma

A

Membrane contains sterols and have no cell walls

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12
Q

Cell wall of Mycobacteria

A

Contains mycolic acid with high lipid content

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13
Q

Bugs that do not gram stain?

A

“These Rascals May Microscopically Lack Color”

Treponema (too thin), Rickettsia (intracellular), Mycobacteria (high lipid content in cell wall), Mycoplasma (no cell wall), Legionella pneumophila (intracellular), Chlamydia (intracellular and lacks muramic acid in cell wall)

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14
Q

Giemsa Stains for what organisms

A

“Certain Bugs Really Try my Patience”

Chlamydia, Borrelia, Rickettsiae, Trypanosomes, Plasmodium

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15
Q

PAS
Name
What does it stain?
Use

A

Periodic Acid Schiff Base
“PASs the sugar”
Glycogen, Mucopolysaccharides
Diagnoses Whipple’s Disease (Tropheryma Whipplei)

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16
Q

Ziehl-Neelsen Stain
Name
Organisms

A

Carbol Fuchsin

Acid Fast organisms (Nocardia, Mycobacterium)

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17
Q

India Ink

A

Cryptococcus neoformans

Mucicarmine can also be used to stain thick polysaccharide capsule red

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18
Q

Silver Stain

A

Fungi, Legionella, Helicobacter pylori

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19
Q

Culture Requirements for H. influenzae

A

Chocolate agar with factor V (NAD) and X (hematin)

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20
Q

Culture Requirements for N gonorrhoeae and N meningitidis

A

Thayer-Martin (or VPN) media

Vancomycin (inhibits Gram+ organisms), Polymyxin (inhibit Gram- organisms except Neisseria), Nystatin (inhibits fungi)

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21
Q

Culture Requirements for B pertussis

A

“Bordet for Bordetella)

Bordet-Gengou (potato) agar

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22
Q

Culture Requirements for C diphtheriae

A

Tellurite plate, Loffler’s media

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23
Q

Culture Requirements for M tuberculosis

A

Lowenstein Jensen agar

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24
Q

Culture Requirements for M pneumoniae

A

Eton’s agar

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25
Q

Culture Requirements for lactose fermenting enterics

A

Pink colonies on MacConkey’s agar (fermentation produces acid, turning colonies pink)
E coli is also grown on eosin-methylene blue (EMB) agar as colonies with green metallic sheen

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26
Q

Culture Requirements for Legionella

A

Charcoal yeast extract on agar buffered with cysteine and iron

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27
Q

Culture Requirements for Fungi

A

“Sab’s a Fun Guy”

Sabouraud’s agar

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28
Q

Obligate Aerobes

A

“Nagging Pests Must Breathe”

Nocardia, Pseudomonas aeruginosa (can use nitrates in anaerobic environment), Mycobacterium tuberculosis, and Bacillus

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29
Q 
Obligate Anaerobes 
Name
Weakness 
Gross 
Culture?
What doe they produce?
Where are they normally?
What antibiotics don't work on them?
A

“Anaerobes Can’t Breathe Air”
Clostridium, Bacteroides, Actinomyces
Lack Catalase and/or SOD and are thus susceptible to oxidative damage
Foul smelling because of short chain fatty acids
Difficult to culture
Produce gas (CO2, H2) in tissue
Normal GI flora
Aminoglycosides ineffective because they need O2 to enter cell

30
Q

Obligate intracellular bugs

A

“Stay inside when its Really Cold”
Rickettsia, Chlamydia
Can’t make their own ATP

31
Q

Facultative Intracellular bugs

A

“Some Nasty Bugs May Live FacultativeLY”

Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francissela, Legionella, Yersinia pestis

32
Q 
Encapsulated Bacteria 
Purpose of capsule 
Test
Examples 
Who is especially at risk?
A

Antiphagocytic virulence factor that can serve as an antigen in vaccines
Quellung Positive (Swelling = Swellung)
“SHiNE SKiS”
Streptococcus pneumoniae, Haemophilus influenzae B, Neisseria meningitidies, E coli, Salmonella, Klebsiella pneumoniae, group B Strep
Asplenics. Give S pneumoniae, H influenzae, and N meningitidis vaccines

33
Q

Catalase+ organisms
Function of catalase
Who is at risk?
Examples

A

Degrades H2O2 before it can become microbicidal
People with chronic granulomatous disease (NADPH oxidase deficiency) because they degrade the limited H2O2
“PLACESS for your CATs”
Pseudomonas, Listeria, Aspergillus, Candida, E coli, S aureus, Serratia

34
Q

Problem with polysaccharide capsule antigens?

How is ti solved?

A 
T cells not activated because polysaccharides cannot be presented 
Conjugate to a protein to promote T cell activation and class switching
35
Q

Pneumovax

A

Polysaccharide vaccine w/o conjugated protein against pneumococcus

36
Q

Prevnar

A

Conjugated Polysaccharide vaccine against pneumococcus

37
Q

H influenzae Type B Vaccine

A

Conjugated vaccine

38
Q

Meningococcal Vaccine

A

Conjugated vaccine

39
Q

Urease+ bugs

A

“CHuck norris hates PUNKSS”

Cryptococcus, H pylori, Proteus, Ureaplasma, Nocardia, Klebsiella, S epidermidis, S saprophyticus

40
Q

Pigment producing bacteria

A

Actinomyces israelii - yellow sulfur granules (israel has yellow sand)
S aureus - yellow pigment
Pseudomonas aeruginosa - blue-green (like arugula)
Serratia marcescens - red pigment (red maraschino cherries)

41
Q

Protein A
Function
Organisms

A

Binds Fc of Ig to prevent opsonization and phagocytosis

S aureus

42
Q

IgA protease
Function
Organisms
Organ susceptible

A

Cleaves IgA
“SHiN”
S pneumoniae, H influenzae B, Neisseria
Respiratory mucosa

43
Q

M Protein
Function
Organisms

A

Prevents phagocytosis

GAS

44
Q 
Exotoxin 
Source
Secreted from cells?
Composition 
Location of gene
Tox
A 
Gram+ and Gram-
Secreted from cells 
Polypeptide 
Plasmid or Bacteriophage 
Highly toxicity
45
Q 
Exotoxin
Antigenicity 
Vaccines
Stability 
Examples
A

Induces high titer Abs called antitoxins
Toxoids used as vaccines
Destroyed rapidly at 60 degrees (except for Staphylococcal enterotoxin)
Tetanus, Botulism, Diphtheria

46
Q 
Endotoxin
Source
Secreted from cells?
Composition 
Location of gene
Tox
A 
Outer cell membrane of most Gram-
Not secreted 
Lipopolysacharide (structural part of bacteria released when lysed)
Bacterial chromosome 
Low toxicity
47
Q 
Endotoxin 
Clinical effects 
MoA 
Antigenicity 
Vaccines
Stability 
Examples
A 
Fever, Shock
Induces TNF and IL1
Poorly antigenic 
No toxoids formed and no vaccine available 
Staple at 100 degrees C for 1 hour
Meningococcemia, Sepsis by Gram- rods
48
Q 
Corynebacterium diphtheriae 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Diphtheria toxin
ADP ribosylating A-B toxin: Inactivates Elongation Factor (EF2) thus inhibiting protein synthesis
Pharyngitis with pseudomembranes in throat and severe lymphadenopathy (bull neck)

49
Q 
Pseudomonas aeruginosa  
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Exotoxin A
ADP ribosylating A-B toxin: Inactivates Elongation Factor (EF2) thus inhibiting protein synthesis
Host cell death

50
Q

ADP ribosylating A-B toxin
Names
MoA

A

Diphtheria toxin, Exotoxin A, Heat Labile, Cholera toxin, Pertussis toxin
B (binding) component binds host cell surface receptor enabling endocytosis; A (active) component attaches to ADP-ribosyl to disrupt host cell proteins

51
Q 
Shigella Spp
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Shiga Toxin (ST)
Inactivates 60S ribosome by removing adenine from rRNA inhibiting protein synthesis
GI mucosal damage –> dysentery. Enhances release of cytokines –> HUS

52
Q 
Enterohemorrhagic E coli (EHEC)
Strain
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A 
O157:H7
Exotoxin
Shiga-Like Toxin (SLT)
Inactivates 60S ribosome by removing adenine from rRNA
Enhances release of cytokines --> HUS 
Does not invade host cells
53
Q 
Enterotoxigenic E coli
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Heat-Labile Toxin (LT) and Heat-Stable Toxin (HS)
HL (ADP ribosylating A-B toxin): Overactivates AC –> ↑cAMP –> ↑Cl secretion in gut and water efflux
HS: Overactivates GC –> ↑cGMP –> ↓ resorption of NaCl and water in the gut
Watery diarrhea
“Labile in Air –> AC”
“Stable in Ground –> GC”

54
Q 
Bacillus Anthracis 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Edema Factor
Mimics AC and increases cAMP
Responsible for characteristic edematous borders of black eschar in cutaneous anthrax

55
Q 
Vibrio cholerae 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Cholera toxin
ADP ribosylating A-B toxin: Permanently activates Gs –> Overactivates AC –> ↑cAMP –> ↑Cl secretion in gut and water efflux
Rice water diarrhea

56
Q 
Bordetella pertusis 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Pertussis toxin
ADP ribosylating A-B toxin: Permanently inactivates Gi –> Overactivates AC –> ↑cAMP –> impaired phagocytosis to permit survival of microbe
Whooping cough (coughs on expiration and whoops on inspiration
100 day cough in adults

57
Q 
Clostridium tetani
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Tetanospasmin
Cleaves SNARE protein required for NT release of GABA and Gly neurons (Renshaw cells in spinal cord)
Muscle rigidity, lock jaw, Risus sardonicus

58
Q 
Clostridium botulinum 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation 
Where do they get it from?
A 
Exotoxin
Botulinum toxin 
Cleaves SNARE protein required for NT release of ACh from neurons 
Flaccid paralysis, floppy baby
Honey
59
Q 
Clostridium perfringens 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Alpha toxin (lecithinase)
Phospholipase that degrades tissues and cell membranes
Degradation of phospholipid C –> myonecrosis (gas gangrene) and hemolysis (double zone of hemolysis on blood agar)

60
Q 
Streptococcus Pyogenes 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Streptolysin O
Degrades cell membranes
Lyses RBCs (contributes to β hemolysis and host produces ASO used to diagnose RF)

61
Q 
Staphylococcus aureus 
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Toxic Shock Syndrome Toxin (TSST1)
Brings together MHCII and TCR to cause release of IFNγ and IL2 –> shock
TSS: fever, rash, shock

62
Q 
Streptococcus pyogenes  
Kind of toxin produced?
Name of toxin?
MoA of toxin 
Manifestation
A

Exotoxin
Exotoxin A
Brings together MHCII and TCR to cause release of IFNγ and IL2 –> shock
TSS: fever, rash, shock

63
Q

Endotoxin Pathway of Action

A

LPS –> Macs –> IL1 (fever), TNF (fever hypotension), NO (hypotension)
LPS –> complement –> C3a (hypotension, edema), C5a (neutrophil chemotactic)
LPS –> tissue factor –> coagulation cascade –> DIC

64
Q

Endotoxin Mnemonic

A

“ENDOTOXIN”

Edema, NO, DIC/Death, Outer membrane, TNFα, O Ag, eXtremely heat stable, IL1, Neutrophil chemotaxis

65
Q

Bacterial Growth Curve

A

Lag: metabolic activity w/o division
Log (exponential): Rapid cell division
Stationary: Nutrient depletion slows growth. Spore formation in some bacteria
Death: Prolonged nutrient depletion and buildup of waste products lead to death

66
Q

Which antibiotics work on the log phase?

A

Cephalosporins and Penicillins becuase they act on peptidoglycan synthesis

67
Q

Bacterial Transformation
Mechanism
Bacteria that can do it?

A

Take up DNA from surroundings
“SHiN”
S pneumoniae, H influenzae, Neisseria

68
Q

Conjugation
F+ x F-
Hfr x F-

A

F+ x F-: dsDNA plasmid with genes for pilus

Hfr x F-: transfer of plasmid and chromosome genes after plasmid incorporation

69
Q

Transposition

A

Segments of DNA jump from one location to another. Genes can be transferred from plasmid to chromosomes and vice versa
Flanking DNA can be transferred as well

70
Q

Transduction
Generalized
Specialized

A

Packaging event: Bacterial DNA packaged into lytic phage by accident
Excision event: Flanking regions around bacterial DNA is put into a Lysogenic phage

71
Q

Genes encoded in lysogenic phage

A

“ABCDE”
shigA-like toxin
Botulinum toxin, Cholera toxin, Diphtheria toxin, Erythrogenic toxin of Strep pyogenes

USMLE STEP 1 (25 decks)

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