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USMLE Step 1-2015 > Microbiology > Flashcards

Microbiology Flashcards

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USMLE® Step 1 flashcards
1
Q

Bugs that do not gram stain well

A

“These microbes may lack real color”

Treponema, Mycobacteria, Mycoplasma, Legionella, Rickettsia, Chlamydia

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2
Q

Giemsa stain

A

“Certain Bugs Really Try my Patience”

Chlamydia, Borrelia, Rickettsia, Trypanosomes, Plasmodium

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3
Q

PAS

A

Stains glycogen (used to diagnose whipple disease (T. Whippeli))

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4
Q

Ziehl-Neelsen (carbol fuchsin)

A

nocardia, mycobacteria (acid fast bacteria), cryptosporidium oocysts (protozoa)

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5
Q

India ink

A

Crytococus neoformans

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6
Q

Sliver stain

A

Fungi (e.g. pneumocystis), Legionella, H. pylori

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7
Q

Alternative to ziehl-neelsen for screening (more sensitive but less specific)

A

Auramine-Rhodamine stain

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8
Q

H influenzae media used for isolation?

Important media contents?

A

Chocolate agar, Factors V (NAD+) and X (hematin)

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9
Q

N gonorrhoeae, N meningitidis media used for isolation?Important media contents?

A

Thayer-Martin, Vancomycin (inhibits gram-positive organisms), Trimethoprim, Colistin (inhibits gram-negative organisms except neisseria), and Nystatin (inhibits fungi)
“Very Typically Cultures Neisseria”

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10
Q

B. pertussis media used for isolation? media contents?

A

1) Bordet-gengou agar (Bordet for bordetella)–>Potato

2) Regan-lowe medium (charcoal, blood, and antibiotic)

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11
Q

C diphtheria media used for isolation?

A

Tellurite agar, Loffler medium

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12
Q

M tuberculosis media used for isolation?

A

Lowenstein-Jensen agar

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13
Q

M. pneumoniae media used for isolation? important media contents?

A

Eaton agar, requires cholesterol

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14
Q

Lactose fermenting enterics media used for isolation? Important media contents/other?

A

MacConkey agar. Fermentation produces acid, causing colonies to turn pink

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15
Q

E. coli media used for isolation? Important media contents/other?

A

Eosin-methylene blue (EMB) agar. Colonies with green metallic sheen

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16
Q

Legionella media used for isolation?

A

Charcoal yeast extract agar buffered with cystein and iron

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17
Q

Fungi media used for isolation?

A

Sabourraud agar “sab’s a fun guy”

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18
Q

Aerobes

A

Nocardia, Pseudomonas, MycoBacterium tuberculosis (Naggigng Pests Must Breathe)

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19
Q

Anaerobes

A

Fusobacterium, Clostridium, Bacteioides, and Actinomyces (Frankly Can’t Breath Air)

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20
Q

What type of drug is ineffective against anaerobes?

A

Aminoglycosides b/c require O2 to enter into bacterial cell

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21
Q

4 key characteristics of anaerobes.

A

1) Suceptible to oxidative damage with no catalase/superoxide dismutase
2) Foul smelling (Short-chain fatty acids)
3) Difficult to culture
4) Produce gas in tissues (CO2 and H2)

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22
Q

Obligate intracellular

A

Rickettsia, CHlamydia, COxiella. Rely on host ATP “Stay inside (cells) when it is Really CHilly and COld”

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23
Q

Facultative intracellular

A

Salmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis (Some Nasty Bugs May Live FacultativeLY)

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24
Q

Encapsulated bacteria

A

SHiNE SKiS
Strep pneumoniae, H. influenzae type B, Neisseria Meningitidis, E. Coli, Salmonella, Kelbseilla pneumoniae, group B Strep

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25
Q

Urease positive organisms

A

Cryptococcus, H pylori, proteus, Ureaplasma, Nocardia, Kebsiella, S epidermidis, S saprophyticus (CHuck Norris hates PUNKSS)

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26
Q

Catalase positive organisms

A

Nocardia, Pseudomonas, Listeria, Aspergillus, Candida, E. coli, Staphylococci, Serratia (Cats Need PLACESS to hide)

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27
Q

Pigment producing bacteria:

Actinomyces israelii–>

A

Yellow “sulfur” granules

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28
Q

Pigment producing bacteria:

S. Auereus–>

A

Yellow pigment

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29
Q

Pigment producing bacteria:

Pseudomonase aeuroginosa–>

A

Blue-green pigment

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30
Q

Pigment producing bacteria:

Serratia marcescens–>

A

Red pigment

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31
Q

IgA protease expressed by?

A

SHiN (includes gonorrhoae and meningitidis here) organisms (IgA protease-enzyme the cleaves IgA)

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32
Q

Protein A expressed by?

A

S. auereus (Protein A-Binds to Fc Region of IgG preventing phagocytosis and opsonization)

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33
Q

M protein expressed by?

A

group A streptococci. M protein helps prevent phagocytosis and share similar epitopes to human cellular proteins (molecular mimicry)

34
Q

Injectisome

A

Certain gram negative bacteria (eg pseudomonas, salmonella, shigella, e. coli)

35
Q

Exotoxin vs Endotoxin species of bacteria it can come from

A

Exotoxin-certain gram + and gram -

Endotoxin-outer cell membrane of most gram -

36
Q

Exotoxin vs Endotoxin. Secreted from cell?

A

Exotoxin-Yes

Endotoxin-No

37
Q

Exotoxin vs Endotoxin. Structure?

A

Exotoxin-Polypeptide

Endotoxin-LPS

38
Q

Exotoxin vs Endotoxin. Location of genes?

A

Exotoxin-Plasmid or bacteriophage

Endotoxin-Bacterial chromosome

39
Q

Exotoxin vs. Endotoxin. Antigenicity?

A

Exotoxin-Induces high-titer antibodies called antitoxins

Endotoxin-poorly antigenic

40
Q

Exotoxin vs. Endotoxin. Vaccines?

A

Exotoxin-Toxoid as vaccine

Endotoxin-No vaccine

41
Q

Exotoxin vs Endotoxin. Heat stability?

A

Exotoxin-destroyed rapidly at 60 degree celsius (ecept staphylococcal enterotoxin and ETEC heat stable toxin)
Endotoxin-Stable at 100 degree celsius for 1 hr

42
Q 
Corynebacterium diphtheria
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Diphtheria toxin
Mechanism-Inhibition of EF-2 (through ribosolation)
Function-Inhibit protein synthesis
Manifestation-pharyngitis with gray pseudomembranes in throat and severe lymphadenopathy (bull neck)

43
Q 
Pseudomonas aeruginosa
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Exotoxin A
Mechanism-Inhibition of EF-2 (through ribosolation)
Function-Inhibit protein synthesis
Manifestation-Host cell death

44
Q 
Shigella spp
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Shiga toxin
Mechanism-Inactivate 60 S ribosome by removing adenine from rRNA (inhibiting protein synthesis and eventual cell death)
Function-Inhibit protein synthesis
Manifestation-GI mucosal damage–> dysentery; Shiga toxin also enchances cytokine release, causing hemolytic uremic syndrome.

45
Q 
Enterohemorrhagic E. coli (EHEC)
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Shiga-like toxin
Mechanism-Inactivate 60 S ribosome by removing adenine from rRNA (inhibiting protein synthesis and eventual cell death)
Function-Inhibit protein synthesis
Manifestation-Cytokine release, causing HUS (prototypically in EHEC serotype 0157: H7). Unlike shigella, EHEC does not invade host cells

46
Q 
Enterotoxigenic E. Coli (ETEC)
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Heat labile toxin
Mechanism- Overactivates adenylate cyclase (increase cAMP)–>increase Cl- secretion in gut and H2O efflux
Function-increase fluid secretion
Manifstation-Watery diarrhea (leading cause of travelers diarrhea)

Toxin-Heat stable toxin
Mechanism-Overactivates guanylate cyclase (increase cGMP)–> decrease resorption of NaCl and H20 in gut
Function-increase fluid secretion
Manifestation-Watery diarrhea( leading cause of travelers diarrhea)

47
Q 
Bacillus anthracis
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Edema toxin (one of 3 components in anthrax toxin)
Mechanism-mimics the adenylate cyclase enzyme (increase cAMP)
Function-increase fluid secretion
Manifestation-responsible for characteristic edematous borders of black eschar in cutaneous anthrax

48
Q 
Vibrio Cholerae
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-cholera toxin
Mechanism-overactivates adenylate cyclase (increase cAMP) by permanently activating Gs–> increase chloride secretion in gut and H20 efflux
Function-increase fluid secretion
Manifestation-voluminous “rice water” diarrhea

49
Q 
Bordetella pertussis
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-pertussis toxin
Mechanism-overactivates adenylate cyclase (increase cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe
Function-inhibit phagocytic ability
Manifestation-Whooping cough (child coughs on expiration and “whoops” on inspiration (toxin may not acutally be a cause of caugh; can cause 100-day cough in adults)

50
Q 
Clostridium tetani
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-tetanospasmin
Mechanism-Cleave SNARE (Soluble NSF attachement protein receptor), a set of proteins required for NT release via vesicular fusion
Function-inhibit NT release
Manifestation-Spasticity, risus sardonicus, and “lockjaw”; toxin prevents release of inhibitory (GABA and glycine) NT from renshaw cells in spinal cord

51
Q 
Clostridium botulinum
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-boutlinum
Mechanism-Cleave SNARE (Soluble NSF attachement protein receptor), a set of proteins required for NT release via vesicular fusion
Function-inhibit NT release
Manifestation-flaccid paralysis, floppy baby; toxin prevents release of stimulatory (Ach) signals at NMJ–>flaccid paralysis

52
Q 
Clostridium perfringens
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Alpha toxin
Mechanism-Phospholipase (lecithinase) that degrades tissue and cell membranes
Function-lyse cell membranes
Manifestation-Phospholipid degradation–>myonecrosis (“gas gangrene”) and hemolysis (“double zone”) of hemolysis on blood agar)

53
Q 
S. pyogenes
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Streptolysin O
Mechanism-Protein that degrades cell membrane
Function-lyse cell membrane
Manifestation-lyses RBCs; contributes to B hemolysis; host antibodies against toxin (ASO) used to diagnose rheumatic fever (do not confuse with immune complexes of poststreptococcal glomerulonephritis)

54
Q 
S. aureus
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-TSST-1
Mechanism-Binds simultaneously to MHC II and TCR outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-gamma and TNF-alpha–>shock
Function-superantigens causing shock
Manifestation-toxic shock syndrome: fever, rash shock; other toxins cause scalded skin syndrome (exfoliative toxin) and food poisoning (enterotoxin)

55
Q 
S. pyogenes
Toxin?
Mechanism?
Function?
Manifestation?
A

Toxin-Exotoxin A
Mechanism-Binds simultaneously to MHC II and TCR outside of antigen binding site to cause overwhelming release of IL-1, IL-2, IFN-gamma and TNF-alpha–>shock
Function-superantigens causing shock
Manifestation: Toxic shock syndrome: fever, rash, shock

56
Q

What does toxin is an ADP ribosylating AB toxin mean?

A

Toxin has two components. A and B. The B (binding) component binds the host cell surface receptor allowing for endocytosis and A (active) component attaches to ADP-ribosyl to disrupt host cell proteins.

57
Q

Addition of what will degrade naked DNA in medium preventing transformation from being seen?

A

Deoxyribonuclease

58
Q

Genes for which 5 bacterial toxins are encoded in a lysogenic phage?

A

(ABCDE)

1) shigA like toxin
2) Botulinum toxin
3) Cholera toxin
4) Diphtheria toxin
5) Erythrogenic toxin of S. pyogenes

59
Q

Some bacteria can form spores at the end of what phase of the bacteria life cycle?

A

Stationary phase when nutrients are limited

60
Q

Spore forming organisms? “BC SPOREadically works in pregnancy?

A

The organisms starting with B or C make spores

Bacillus anthracis, Bacillus cereus, Clostridium botulinum, dificile, perfringens, tetani, Coxiella burnetti

61
Q

Lactose fermenting enteric bacteria that cause pink colonies on MaConkey agar

A

Citrobacter, Kelbsiella, E. coli, Enterobacter, and Serratia (weak fermenter)
“macConKEES”

62
Q

EMB agar has lactose fermenters grow as what and what is the unique exception?

A

Lactose fermenters grow as purple/black colonies. E. coli grows colonies with a green sheen.

63
Q

Spirochetes: Sprial shaped bacteria with axial filaments

A

Borrelia (big size, Leptospira, and Treponema (Boars leaped and tripped on him)

64
Q

False- positive on VDRL

A

Viral infection (mono, hepatitis), Drugs, Rheumatic fever, Lupus and leprosy (VDRL)

65
Q

Anaplasma species
Disease?
Transmission and source?

A 
Anaplasmosis
Ixodes ticks (live on deer and mice)
66
Q

Bartonella species
Disease?
Transmission and source?

A

Cat scratch disease (immunocompetant), bacillary angiomatosis (immunocompromised)
Cat scratch

67
Q

Borrelia bugdorferi
DiseasE?
Transmission and source?

A 
Lyme disease
Ixodes ticks (live on deer and mice)
68
Q

Borrelia recurrentis
Disease?
Transmission and source?

A

Relapsing fever

Louse (recurrent due to variable surface antigens)

69
Q

Campylobacter
Disease?
Transmission and source?

A

Bloody diarrhea

Puppies, livestock (fecal oral, ingestion of undercooked meat)

70
Q

Chlamydophila psittaci
Disease?
Transmission and source?

A

Psittacosis

Parrots, other birds

71
Q

Coxiella burnetii
Disease?
Transmission and source?

A

Q fever

Aerosols of cattle/sheep amniotic fluid

72
Q

Ehrlichia chaffeensis
Disease?
Transmission and source?

A

Ehrlichiosis

Ambylomma (lone star tick)

73
Q

Francisella tularensis
DiseasE?
Transmission and source?

A

Tularemia

Ticks, rabbits, deer fly

74
Q

Leptospira spp.
Disease?
Transmission and source?

A

Leptospirosis

Animal urine

75
Q

Mycobacterium leprae
Disease?
Transmission and source?

A

Leprosy

Humans with lepromatous leproy; armadillo (rare)

76
Q

Pasteurella multocida
Disease?
Transmission and source?

A

Cellulitis, osteomyelitis

Animal bite, cat, dogs

77
Q

Rickettsia prowazekii
Disease?
Transmission and source?

A

Epidemic typhus

Louse

78
Q

Rickettsia rickettsii
Disease?
Source?

A

Rocky mountain spotted fever

Dermacentor (dog tick)

79
Q

Rickettsia typhi
Disease?
Source?

A

Endemic typhus

Fleas

80
Q

Salmonella
Disease?
Source?

A

Diarrhea (which may be bloody), vomiting, fever, abdominal cramps
Reptiles and poultry

81
Q

Yersenia pestis
Disease?
Source?

A 
Plague
Fleas (rats and prarie dogs are reservoirs)
82
Q

Brucella species
Disease?
Source?

A

Brucellosis/undulant (rising and falling) fever, spread to reticuloendothelial organs (liver, spleen) causing enlargement
Unpasteurized dairy, farm animals

USMLE Step 1-2015 (18 decks)

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