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USMLE Step 1 > Microbiology > Flashcards

Microbiology Flashcards

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USMLE® Step 1 flashcards
1
Q

How does gonorrhea cause recurrent infections?

A

Its pili undergoes antigenic and phase variation

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2
Q

What’s pathognomonic for Human Granulocyte Anaplasmosis?

A

Morulae (berry-like) clusters of the intracellular orgs

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3
Q

Which orgs have the Ixodes tick as their vector?

A 
Anaplasma
\+
Borrelia burgdorferi
\+
Babesia microti
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4
Q

Which orgs have the louse as their vector?

A

Borrelia recurrentis
+
Rickettsia prowazekii

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5
Q

Which orgs have the Dermacentor tick as their vector?

A

Francisella tularensis
+
Rickettsia rickettsii

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6
Q

Which orgs have the flea as their vector?

A

Rickettsia typhi
+
Yersinia pestis

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7
Q

What is a characteristic histological trait for CMV?

A

Owl-eye inclusion (singular)

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8
Q

How does cryptosporidium cause diarrhea in AIDS pts?

A

Intracellular multiplication in the brush border

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9
Q

Under which circumstances do M. tuberculosis and M. avium-intracellulare infect AIDS pts?

A

TB = CD >400

M. avium = CD

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10
Q

How do you test for Mono (EBV)?

A

Monospot test: heterophile antibody test

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11
Q

What characteristic differentiates Campylobacter jejuni from other diarrhea-causing organisms?

A

Growth at 42C

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12
Q

What is the virulence factor for C. diptheriae? and what does it do?

A

Exotoxin encoded by beta-prophage DNA;

inhibits protein synthesis by ADP-ribosylation of eEF-2

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13
Q

How does anaerobic bacteroides infection present in alcoholics?

A

rust-colored sputum from aspiration pneumo (normal oral flora causing lung abscesses)

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14
Q

How does toxoplasmosis manifest in IC pt?

A

reactivation of latent infection =

-multiple ring-enhacing lesions on CT but no neuro symps

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15
Q

Whats the serology for acute HBV infection?

A

HB-s-Ag
HB-e-Ag
anti-HB-c-IgM Ab

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16
Q

What is the clinical manifestation of H. ducreyi?

A

papule w red base that progresses to painful ulcer (chancroid) and inguinal adenopathy

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17
Q

What are the hallmarks of actinomyces infection?

A
  • branching rods
  • sulfur granules
  • IUD
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18
Q

What is a parasitic risk factor for pigmented gallstones?

A

chlonorchis sinensis (oriental liver fluke)

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19
Q

What are key symptoms of bordatella pertussis infection?

A

whooping cough and hypoglycemia

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20
Q

What are the hallmarks of atypical “walking” pneumo?

A

mycoplasma pneumo = cold agglutinins (IgM)

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21
Q

What is a diagnostic marker for E. histolytica?

A

Cysts with up to 4 nuclei + RBCs in the cytoplasm

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22
Q

What org is the most common cause of pseudoappendicitis in the US and what is its cause?

A

Yersinia enterocolitica; transmitted via contaminated milk or pork

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23
Q

What virulence factor causes the fever and rash in Scarlet fever?

A

pyrogenic exotoxins A-C

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24
Q

When an HIV+ person enters early symptomatic stage, what happens to their levels of anti-p24?

A

Decreases bc immune system loses ability to make antibodies

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25
Q

What phase of the bacterial growth curve has the greatest spore production?

A

Stationary phase (F)

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26
Q

How does pseudomonas exotoxin A work? and what other org works the same way?

A

inhibits protein synthesis by ADP-ribosylation of eEF-2;

C. diptheriae

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27
Q

What mechanism mediates resistance to aminoglycosides?

A

enzymatic inactivation

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28
Q

Whats the most important virulence factor in E. coli that causes neonatal meningitis?

A

K1 capsule

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29
Q

Where in the brain does neonatal herpes encephalitis usually manifest?

A

temporal lobes (bilaterally)

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30
Q

Tests for Hep B in pregnant woman?

A

HBsAg: - = recovered, + = carrier

IgG for HBsAg: + = immunity/recovery

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31
Q

Which bacterial toxins are expressed by lysogenic conversion?

A 
COBEDS:
Cholera
O toxin of Salmonella
Botulinum toxin
Erythrogenic toxin of S. pyogenes
Diptheria toxin
Shiga toxin
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32
Q

What is the key virulence factor in G- bacteria?

A

Lipid A in LPS

O is the antigen = immunity

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33
Q

How to tell generalized v specialized transduction?

A 
generalized = lytic phage
specialized = lysogenic phage (near insertion site)
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34
Q

Which C. perfringens toxin in assoc w gas gangrene?

A

Alpha toxin

35
Q

Whats the major difference between s. aureus pneumo and strep pneumo?

A

s. aureus pneumo = cavitary lesion

36
Q

Describe cat-scratch disease?

A

Cause: bartonella henselae from cats (esp kittens)
hallmarks: papule w regional lymphadenopathy
Histo: stellate granulomas

37
Q

What is the HepB window period?

A

When neither HBsAg nor HBsAb can be detected.

38
Q

What is the Ghon complex?

A

Primary TB infection w granulomas in mid zone of lung + hilar nodes

39
Q

Any obstructive lesion in urinary tract (esp in older adults) indicates what bacteria?

A

E. coli (can lead to bacteremia and ARDS)

40
Q

What parasites cause calcifying lung masses in IC pts? and how do you tell them apart?

A

Histoplasma (small yeasts in macros, Midwest) or Blastocyes (broard-based yeast, Eastern US)

41
Q

On what medium does the genus Vibrio grow on?

A

alkaline medium

42
Q

Which organisms are encapsulated?

A 
Some Killers Have Pretty Nice Capsules:
Strep pneumo
Klebsiella
H. flu
Pseudomonas
Neisseria
Cryptococcus
43
Q

What is the histological hallmark for P. vivax/ovale?

A

Schuffner dots = oval body w brick-red dots in RBCs

Note: vivax only occurs in Panama

44
Q

What are the clinical manifestations of lyme disease years after the tick bite?

A

MSK: monoarthritis (knees)
Neuro: Bell’s palsy

45
Q

What are the taxonomic characterisitics of B. anthracis?

A

G+ rod; box-car shaped; aerobic; spore-forming

46
Q

What is Reiter Syndrome and its symtpoms?

A 
Autoimmune rxm to previous infection of:
Campylobacter
Chlamydia
Yersinia
Salmonella
Shigella

Symptoms (triad): arthritis, urethritis, conjunctivitis

47
Q

Describe molluscum contangiosum.

A

Benign, self-limiting umbilicated warts in school children from Poxvirus

48
Q

What is the most common cause of bloody diarrhea in the US?

A

Shigella

49
Q

What is the first thing RSV does when it enters a cell?

A

Creates complimentary copy of its genome using RNA-dep-RNA-poly

50
Q

What is the most common means of transmission for toxoplasmosis in the US?

A

Cysts from undercooked pork

51
Q

What parasite is associated w Vit B12 def with macrocytic anemia?

A

Diphyllobothrium latum from freshwater fish (Great Lakes tapeworm)

52
Q

Pregnant woman with CMV infection will have which symptoms?

A

flu-like: mild fever, generalized lymphadenopathy

53
Q

What causes blister-like lesions that progress to yellow crust?

A

Non-bullous impetigo (s. aureus or s. pyogenes)

54
Q

What’s the difference between bullous and non-bullous impetigo?

A 
bullous = s. aureus; brown crust
non-bullous = aureus/pyogenes; yellow crust
55
Q

What organism causes food poisoning from pastries, poultry, eggs, salad in just a few hours?

A

s. aureus via enterotoxin A

56
Q

What orgs cause atypical pneumo in adults?

A

myco pneumo: non-productive cough
legionella: ac, smoking
chlam psittaci: birds, hepatitis
p. jirovecii: AIDs

57
Q

What are the hallmarks of Paracoccidioidomycosis?

A
  • Latin America

- budding yeast w “Captain’s wheel” formation

58
Q

Which bacteria are natural transformers?

A

H. flu
Strep pneumo
Neisseria

59
Q

What org associates colon cancer with endocarditis?

A

Strep bovis

60
Q

Which virus families have a segmented genome?

A 
ROBA:
Rotavirus
Orthomyxo
Bunya
Arena
61
Q

Describe JC virus reactivation in AIDS pts.

A

Progressive multifocal leukoencephalopathy = nonenhancing areas of demyelination on MRI

62
Q

What are the hallmarks of a premature infant pneumocystis pneumo?

A

P. jirovecii = surfectant-rich exudate w cysts that stain w methenamine silver

63
Q

What is giardia lambia’s key mode of pathogenesis?

A

Adherence to mucosal surface via ventral sucking disk (never penetrates the bowel)

64
Q

UTI w (+)leukocyte esterase and (-)nitritrie indicates what organism?

A

Enterococcus faecalis or S. saprophyticus

65
Q

Which hepatitis has the highest mortality amongst pregnant women?

A

Hep E (hep-e-viridae)

66
Q

What org is the most common cause of epiglottitis?

A

H. influenza

67
Q

What kind of vaccine is used against H. flu?

A

toxoid + polyribitol phosphate capsular polysaccharide

68
Q

Which org is the leading cause of shellfish-related deaths in the US?

A

Vibrio vulnificus (others: Vibrio parahaemolyticus, Hep A)

69
Q

Which org infects AIDS pts with CD

A

CD

70
Q

What feature of M. tuberculosis causes a (+) PPD test?

A

Outer surface protein tuberculin

71
Q

How do enterococcal species gain penicillin and tetracycline resistance?

A

transposons

72
Q

What is the best test to diagnose p. jirovecii infection?

A

Direct fluorescent antibody test

73
Q

Why are antibodies against Mumps ineffective?

A

They transfer from cell-to-cell via syncytia and thus, are never exposed outside of cell
-need cell-mediated immunity

74
Q

How do macrolides (-mycin) work?

A

Interferes with translocation by binding 23s (50s)

75
Q

Lacey EBV cells are derived from which type of cell?

A

Reactive cytotoxic T cells

76
Q

Org causes vegetation on tricuspid valve on echocardiography?

A

s. aureus

77
Q

How do you know if a protease inhibitor is working?

A

There is a lack of a mature core (which requires protease in order to be formed)

78
Q

What is the virulence factor for E.coli in UTIs?

A

p-pili (adhesins), allow them to adhere to urinary tract

79
Q

Neuraminidase inhibitor mechanism of action?

A

prevents release of virus from infected epithelial cells

80
Q

Whats the MOA for fluoroquinolones?

A

inhibiting DNA gyrase

81
Q

Treatment for all Rickettsial and vector-borne illnesses?

A

Doxycycline

82
Q

Why does M. leprae infect the skin and not visceral organs?

A

It prefers cooler temps

Reservoir = armadillos

83
Q

What makes up the pseudomembrane on c.diff colitis?

A

inflammatory cells + fibrin + necrotic cells

USMLE Step 1 (13 decks)

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