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USMLE STEP 1 > Micro > Flashcards

Micro Flashcards

1
Q

peptidoglycan

A

sugar backbone cross-linked by transpeptidase

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2
Q

gram positive cell wall

A

lipoteichoic acid (induces TNF and IL-1)

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3
Q

gram negatives outer membrane

A

site of endotoxin (LPS); lipid A induces TNF and IL-1; O polysaccharide is the antigen

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4
Q

periplasm

A

contains beta lactamases; space between cytoplasmic and outer membranes in gram negatives

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5
Q

capsule

A

polysaccharide (except B. anthracis, which contains D-glutamate)

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6
Q

glycocalyx

A

polysaccharide which mediates adherence to foreign surfaces

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7
Q

contain sterols and no cell wall

A

mycoplasma

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8
Q

contain mycolic acid

A

mycobacteria

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9
Q

common infection forming intraabdominal abscess

A

bacteroides fragils

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10
Q

bugs that do not gram stain well

A

Treponema (dark-field microscopy, fluorescent Ab), Rickettsia (intracellular), mycobacteria (carbolfuchsin in acid-fast), mycoplasma, legionella pneumophila (silver stain), chlamydia (intracelluar, lacks muramic acid)

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11
Q

Giemsa stain

A

chlamydia, borrelia, rickettsiae, trypanosomes, plasmodium

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12
Q

PAS

A

stains glycogen; used to diagnose Whipple’s disease

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13
Q

Ziehl-Neelsen

A

nocardia, mycobacterium

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14
Q

india ink

A

cryptococcus neoformans

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15
Q

silver stain

A

fungi, legionella, H. pylori

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16
Q

H. influenza culture

A

chocolate agar with factors V (NAD+) and X (hematin)

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17
Q

N. gonorrhoeae, N. meningitidis culture

A

Thayer-Martin (VPM): vancomycin, polymyxin, nystatin

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18
Q

B.pertussis culture

A

Bordet-Gengou agar

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19
Q

C. diphtheriae culture

A

Tellurite plate, Loffler’s media

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20
Q

M. TB culture

A

Lowenstein-Jensen agar

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21
Q

M. pneumoniae culture

A

Eaton’s agar

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22
Q

lactose-fermenting enterics culture

A

pink colonies; E. coli also grown on eosin-methylene blue agar

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23
Q

legionella culture

A

charcoal yeast buffered with cysteine and iron

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24
Q

fungi culture

A

sabouraud’s agar

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25
Q

obligate aerobes

A

nocardia, pseudomonas (may use nitrates as terminal electron acceptors in environments with low O2), mycobacterium TB, bacillus

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26
Q

obligate anaerobes

A

clostridium, bacteroides, actinomyces; lack catalase and/or superoxide dismutase

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27
Q

aminoglycosides against anaerobes

A

not effective (reguire O2 to enter into bacterial cell)

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28
Q

obligate intracellular bugs

A

rickettsia, chlamydia

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29
Q

facultative intracellular bugs

A

salmonella, neisseria, brucella, mycobacterium, listeria, francisella, legionella, yersenia

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30
Q

encapsulated bacteria

A

positive quellung reaction; strep pneumonia, H. influenza type B, neisseria meningitidis, E. coli, salmonella, klebsiella pneumonia, group B strep

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31
Q

catalase-positive organisms

A

pseudomonas, listeria, aspergillus, candida, E. coli, S. aureus, serratia; pts with chronic granulomatous disease (NADPH oxidase deficiency) have recurrent infections

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32
Q

urease-positive bugs

A

cryptococcus, H. pylori, proteus, ureaplasma, nocardia, klebsiella, S. epidermidis, S. saprophyticus

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33
Q

actinomyces israelii pigment

A

yellow sulfur granules

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34
Q

s. aureus pigment

A

yellow

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35
Q

pseudomonas pigment

A

blue-green

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36
Q

serratia marcescenes pigment

A

red

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37
Q

protein A

A

binds Fc portion of Ig; S. aureus

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38
Q

IgA protease

A

S. pneumonia, H. influenza type B, Neisseria

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39
Q

M protein

A

group A strep

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40
Q

live attenuated vaccine

A

more effective in generating prolonged mucosal IgA secretion than killed vaccine

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41
Q

corynebacterium diphtheriae toxin

A

diphtheria toxin (ADP ribosylating AB toxin); inactivates elongation factor 2–>inhibits protein synthesis; pharyngitis with pseudomembranes and severe lymphadenopathy

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42
Q

pseudomonas toxin

A

exotoxin A (ADP ribosylating AB toxin); inactivate elongation factor 2–> inhibit protein synthesis

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43
Q

shigella toxin

A

shiga toxin (AB); inactivates 60S ribosome (removes adenine from rRNA, lyses 28sRNA)–>inhibits protein synthesis; GI mucosal damage, enhances cytokine release–>HUS

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44
Q

EHEC toxin

A

shiga-like toxin; inctivates 60S–>inhibits protein synthesis; does not invate host cells unlike shigella

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45
Q

ETEC toxin

A

heat-labile: increased cAMP–>increased Cl- secretion; heat-stable: increased cGMP–> decreased resoprtion of NaCl

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46
Q

bacillus anthracis toxin

A

edema factor; increases cAMP; black eschar

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47
Q

vibrio cholerae toxin

A

cholera toxin (affects apical ion transport); increased cAMP (permanentaly activates Gs)–> increased Cl- secretion; rice-water diarrhea

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48
Q

bordetella pertussis toxin

A

pertussis toxin; increased cAMP (disables Gi)–> impairs phagocytosisl whooping cough: cough on expiration and whoops on inspiration

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49
Q

clostridium tetani toxin

A

tetanospasmin; cleave SNARE; muscle rigidity, lock-jaw, inhibits release of inhibitory NT

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50
Q

clostridium botulinum toxin

A

botulinum toxin; cleaves SNARE; flaccid paralysis, floppy baby, prevents release of ACh

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51
Q

clostridium oerfringens toxin

A

alpha toxin (phospholipase that degrades tissue and cell membranes); degradation of phospholipid C–>myonecrosis and hemolysis

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52
Q

strep. pyogenes toxin

A

streptolysin O (protein that degrades cell membranes); lyses RBCs; host Ab against toxin (ASO) used to diagnose rheumatic fever

53
Q

staph aureus toxin

A

toxic shock syndrome toxin; bring MHC II and TCR in proximity to outside of antigen-binding site–>release of IFN gamma and IL-2; toxic shock syndrome, scalded skin syndrome

54
Q

strep pyogenes superantigen toxin

A

exotoxin A; bring MHC II and TCR in proximity to outside of antigen binding site–>release of IFN gamma and IL-2; toxic shock syndrome

55
Q

which phase of bacterial growth do penicillins and cephalosporins act on

A

exponential/log

56
Q

transformation

A

ability to take up naked DNA; Strep pneumonia, H. influenza type B, Neisseria; add deoxyribonuclease to environment–>no transformation

57
Q

conjugation

A

transfer of plasmid, no transfer of chromosomal genes

58
Q

F+ plasmid

A

can become incorporated into chromosomal DNA

59
Q

transposition

A

excision and reintegration of segment DNA

60
Q

generalized transduction

A

lytic phage infects bacterium–>parts of bacterial chromosomal DNA become packaged into viral capsid–>phage infects another becterium, transferring genes

61
Q

specialized transduction

A

viral DNA incorporates into bacterial chromosome

62
Q

toxins acquired through specialized transduction

A

shiga-like toxin, botulinum, cholera, diphtheria, erythrogenic toxin of Strep pyogenes

63
Q

gram positive, branching filaments, anaerobe, not acid fast

A

actinomyces

64
Q

gram positive, branching filaments, aerobe, acid fast

A

nocardia

65
Q

gram positive, cocci, catalase positive

A

staph

66
Q

gram positive, cocci, catalase negative

A

strep

67
Q

coagulase positive staph

A

S. aureus

68
Q

coagulase negative staph, novobiocin sensitive

A

S. epidermidis

69
Q

coagulase negative staph, novobiocin resistant

A

S. saphrophyticus

70
Q

alpha hemolytic strep, capsule, optochin sensitive

A

S.pneumonia

71
Q

alpha hemolytic strep, no capsule, optochin resistant

A

viridans strep (S. mutans)

72
Q

beta hemolytic strep, group A, bacitracin sensitive

A

S. pyogenes

73
Q

beta hemolytic strep, group B, bacitracin resistant

A

S. agalactiae

74
Q

gamma hemolytic strep, group D, growth in bile and 6.5% NaCl

A

enterococcus (E. faecalis)

75
Q

gamma hemolytic strep, growth in bile, not 6.5% NaCl

A

nonenterococcus (S. bovis)

76
Q

beta hemolytic bacteria

A

S. aureus, Strep pyogenes, Strep agalactiae, Listeria monocytogenes

77
Q

S. aureus

A

gram + cocci, protein A binds Fc-IgG inhibiting complement fixation; forms fibrin clot around self–>can lead to abscess

78
Q

S. aureus spread

A

traumatic wound–>leaking CSF–>meninges

79
Q

MRSA

A

resistant to beta lactams because of altered penicillin-binding protein

80
Q

staph. epidermidis

A

catalase +, coagulase -, novobiocin sensitive; associated with ventriculoperitoneal shunts; produces adherent biofilms (extracellular polysaccharide matrix)

81
Q

empiric treatment for staph. epidermidis

A

vancomycin

82
Q

strep. pneumonia

A

most common cause of meningitis, otitis media, pneumonia, sinusitis; lancet-shaped , gram + diplococci, encapsulated, IgA protease; optochin sensitive, lysed by bile

83
Q

strep pneumonia spread

A

middle ear–>contiguous tissue–>meninges; primary lung focus–>blood–>meninges

84
Q

viridans group strep

A

alpha hemolytic, resistant to optochin; can produce extracellular polysaccharides (dextrans)–>facilitate strep adherens to fibrin (must have pre-existing endothelial damage); not lysed by bile

85
Q

strep pyogenes

A

beta hemolytic, bacitracin sensitive. Ab to M protein enhance host defenses–>can give rheumatic fever

86
Q

what detects recent strep. pyogenes infection?

A

ASO titer

87
Q

strep. agalactiae

A

bacitracin resistant, beta hemolytic; produces CAMP factor (enlarges area of hemolysis formed by S. aureus). Hippurate test positive

88
Q

CAMP test

A

detects incomplete hemolysin

89
Q

enterococci (group D strep)

A

normal colonic flora; cause UTI, biliary tract infections, subacute endocarditis; can grow in 6.5% NaCl and bile

90
Q

strep bovis (group D strep)

A

can cause bacteremia and subacute endocarditis in colon cancer pts

91
Q

corynebacterium diphtheriae

A

exotoxin encoded by bate prophage; inhibits protein synthesis via ADP-ribosylation of EF-2; pseudomembranous pharyngitis with lymphadenopathy, myocarditis, arrhythmia

92
Q

gram + rods with metachromatic granules and Elek’s test for toxin

A

corynebacterium diphtheriae

93
Q

toxoid vaccine

A

prevents diphtheria; IgG against exotoxin B subunit

94
Q

black colonies on cystine-tellurite agar

A

corynebacterium diphtheria

95
Q

have dipicolinic aicd in their core

A

spores

96
Q

gram positive, spore-forming, obligate anaerobic bacilli

A

clostridia

97
Q

C. tetani

A

toxin (and botulinum toxin) is a protease that cleaves releasing proteins for neurotransmitters; blocks glycine and GABA release; immunized mother can pass IgG to fetus to provide passive immunity

98
Q

C. tetani spread

A

wound–>motor neuron axons–>spinal cord

99
Q

C. botulinum

A

heat-labile toxin that inhibits ACh release; bilateral descending muscle weakness, diplopia, dysphagia, dysphonia

100
Q

C. perfringes

A

produces alpha toxin (lecithinase); loss of cell membrane integrity, can cause diarrhea from meat

101
Q

C. difficile

A

AB toxin (B destroys cytoskeletal structure)–>pseudomembranous colitis; secondary to clindamycin or ampicillin

102
Q

C. difficile treatment

A

metronidazole or vanco

103
Q

neonatal tetanus

A

usually results from C. tetani colonization of umbilical stump

104
Q

anthrax

A

gram + spore-forming rod; only bacterium with polypeptide capsule (contains D-glutamate)

105
Q

baccilus cereus

A

food poisoning (reheated rice syndrome); nausea and vomiting caused by cereulide

106
Q

listeria monocytogens

A

gram +, beta hemolytic, blue-green transluscent colonies, intracellular growth; transmission from unpasteurized milk or vaginal

107
Q

forms actin rockets, tumbling motility

A

listeria monocytogens

108
Q

listeria monocytogens diseases

A

spontaneous abortion, granulomatosis infantiseptica, neonatal meningitis, mild gastroenteritis. Treat neonates and immunocompromised with ampicillin

109
Q

actinomyces

A

gram + rod anaerobe, not acid fast; oral/facial abscesses; treat with penicillin

110
Q

nocardia

A

gram+ aerobe, acid fast; pulmonary and cutaneous infections; treat with sulfonamides

111
Q

mycobacteria TB

A

phagocytosed by alveolar macrophages and sulfatide virulence factor allows for intracellular bacterial proliferation; never treated as monotherapy due to resistance

112
Q

TB immune reaction

A

TH1-mediated; primary: CD4+ TH1, lymphocytes, macrophages

113
Q

M. avium

A

causes disseminated non-TB disease in AIDS. prophylaxis with azithromycin

114
Q

cord factor

A

in virulent TB strains; inhibits macrophage stimulation and induces release of TNF alpha

115
Q

M. TB spread

A

primary lung focus–>blood–>meninges

116
Q

acid fast bacillus that likes cool temperatures

A

mycobacterium leprae

117
Q

lepromatous form

A

diffuse over skin; low cell-mediated immunity with TH2 response; functionally defective macrophages

118
Q

tuberculoid form

A

a few hairless skin plaques; high cell-mediated immunity with largely CD4+ TH1 response; lepromin skin test is positive

119
Q

tuberculoid form treatment

A

dapsone and rifampin for 6 months

120
Q

lepromatous form treatment

A

dapsone, rifampin, clofazimine for 2-5 years

121
Q

gram -, oxidase +, comma shaped, grows in 42 degrees

A

campylobacter jejuni

122
Q

gram -, oxidase +, comma shaped, grows in alkaline media

A

vibrio chlerae

123
Q

gram - diplococci, maltose fermenter

A

N. meningitidis

124
Q

gram - diplococci, maltose nonfermenter

A

N. gonorrhoeae

125
Q

gram - rod, lactose nonfermenter, oxidase -

A

shigella, salmonella, proteus

126
Q

gram - rod, lactose nonfermenter, oxidase +

A

pseudomonas, H. pylori

127
Q

lactose-fermenting enteric bacteria

A

klebsiella, e. coli, enterobacter, citrobacter, serratia

128
Q

produces beta galactosidase, which breaks down lactose into glucose and galactose

A

E. coli

USMLE STEP 1 (21 decks)

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