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USMLE/ Step ONE > MICRO > Flashcards

MICRO Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the GP rods/bacilli?

A 
Clostridium
Bacillus
Corynebacterium
Listeria
Mycobacterium
Gardnerella
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2
Q

What are the branching filamentous bacteria?

How do they gram stain?

A

Actinomyces & Nocardia

Gram positive

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3
Q

Which bacteria does not have a cell wall?

How does it gram stain?

A

Mycoplasma. Does not gram stain!

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4
Q

What is PG of bacteria made of? What enzyme significant to structure

A

Sugar backbone w/ peptide side chains, crosslinked by transpeptidase

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5
Q

Differentiate GP vs GN bug wall structure

A

GP: Lipoteichoic acid, thicker PG layer
GN: LPS/Endotoxin, periplasm, thin PG layer

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6
Q

What induces TNF & IL-1 in GN & GPs?

A

GP: Lipoteichoic acid
GN: Lipid A

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7
Q

What are capsule made of? What is the exception

A

Polysacharide

(EXCEPTION: Bacillus anthracis contains D-glutamate, a Polypeptide)

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8
Q

What structure allows bugs to adhere to foreign substances?

A

Glycocalyx

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9
Q

normal flora for skin?

A

Staph epidermidis

S. aureus, yeasts, & other strep species

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10
Q

normal flora for mouth (oropharynx)?

A

Viridins strep (Strep mutans), Candida, H. influenza (type w/o capsule), Neisseria

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11
Q

normal flora of adult colon?

A

Bacteroides fragilis > E. coli

Fusobacterium, Lactobacillus,Enterococcus faecalis, GN anaerobic rods

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12
Q

normal flora in baby colon? (being breast-fed)

A

Bifidobacterium

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13
Q

normal flora in vagina?

A

Lactobacillus. E. coli, group B strep, Corynebacterium, Candida

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14
Q

MC cause of neonatal meningitis? MC transmission source?

A

Group B strep! During natural delivery, from vagina normal flora

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15
Q

List the 3 main causes of newborn (0-6mon) meningitis

A

1) Group B strep
2) E. coli
3) Listeria

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16
Q

what is polycistronic mRNA and give example? Where is it found?

A

single mRNA can code for several genes. Found in Prokaryotes, NOT Eukaryotes.

Ex; Lac operon in E. coli

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17
Q

How does bacteria replicate?

A

Binary fission asexual

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18
Q

What component of Fungal cell membrane target of drugs (different from bacteria)?

A

Ergosterol

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19
Q

normal flora of body organs?

A

NONE! Sterile, like blood should be

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20
Q

name the one bug that can replicate in stomach?

A

H pylori

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21
Q

virulence factor for E. coli to cause UTI? What type of bugs this found?

A

Pili! How it clings to urethra against urine stream

Pili found in GN bugs

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22
Q

Explain chronic infection by Neisseria?

A

Pili change to avert immune response = antigenic variation

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23
Q

Adherence structure for GP bugs?

A

Teichoic acids

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24
Q

Adhesions are important virulence factor for which toxins?

A

pertussis & hemagglutinins

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25
Q

Which bugs use IgA protease?

A

Strep pneumo
H. influenza type B
Neisseria

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26
Q

Obligate aerobe w/ a capsule?

A

Pseuodomonas aeruginosa

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27
Q

Fungi w/ a capsule?

A

Cryptococcus neoformans

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28
Q

MC virulence factor of bacterial meningitus?

A

Capsules! help to cross BBB (very slippery) & evade immune response

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29
Q

Anti-phagocytis virulence factors w/ associated bugs

A

Protein A- S. aureus
M protein- GAS
Pili- N. gonorrhea

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30
Q

What bugs do phase variation?

A

Trypanosoma brucei rhodesiense &

Trypanosoma brucei gambiense

31
Q

Phase variation in flagella?

A

Enterobacteriaceae

32
Q

what tests used to detect capsule?

A

Quelling reaction and Latex particle agglutination

33
Q

Which bugs are intracellular- facultative?

A 
Salmonella
Neisseria
Brucella
Listeria
Francisella
Legionella
Yersina
Mycobacterium
34
Q

Obligate intracellular bugs?

A

Chlamydia & Rickettsia

35
Q

Describe intracellular mechanisms of TB & Listeria?

A

TB: (-) phagolysosome fusion

Listeria- leaves phagosome before phagolysosome fusion

36
Q

How does a bug invade a non-phagocytic cell?

A

Invasins

37
Q

Patient has Chronic Granulomatous Disease. Increased risk of infection by…?

A

Catalase + bugs!

SPACE MaN SaM
S. aureus, Pseudomonas, Aspergillus, Candida, E. coli, Mycobcaterium, Nocardia, Serratia marcescens

38
Q

Obligate aerobes ? Fermentation method?

A

Nocardia
TB
Pseudomonas aeruginosa
Bacillus

No fermentation

39
Q

When do you see infection by Pseudomonas aeruginosa?

A

Diabetes
Burn wounds
Nosocomial pneumonia
CF patients w/ pneumonia

40
Q

Urease + bugs

A

CHuck norris hates PUNKSS

Cryptococcus
H. pylori
Proteus
Ureaplasma
Nocardia
Klebsiella
S. epidermidis
S. saprophticus
41
Q

Describe how vaccines made for capsular bugs?

A

Capsules (polysaccharide) are conjugated to a protein (i.e. Prevnar). This promotes Tcell activation and later class switching. If not conjugated, only IgM abs made

42
Q

Type III secretion system? Bugs?

A

Tunnel from bug to macrophage to inject toxins

E. coli, Salmonella, Yersinia, Chlamydia, Pseudomonas

43
Q

Rheumatic fever example of what HS?

A

Type 2

Cross reaction of bacterial-induced Abs w/ tissue Ags (endoderm)

44
Q

Granulomas seen in what type of bugs? What type of HS?

A 
Intracellular facultative
Type 4 (DTH)
45
Q

Virulence factors of TB?

A

Nothing release. The immune response is what is damaging

46
Q

Which organism can block the bile duct?

A

Ascaris worm

47
Q

Heat stability of toxins?

A

Exo are destroyed @ 60C, except enterotoxin by Staph

Endo stable @ 100C for an hour

48
Q

Endo vs Exotoxin: secretion

A

Exo are secreted, Endo not secreted

49
Q

Toxin vaccination for Endo and Exo

A

Vaccines for Exotoxins using toxoids

NONE for Endo

50
Q

Which bugs are Beta-hemolytics?

A

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

51
Q

Coagulase pos, GP cocci virulence factors? How

A 
Protein A- 
(-) phago & complement fixation
TSST
Enterotoxin
Catalase, Coagulase
Exfoliative toxin
Alpha-toxin (makes cell pores)
52
Q

GP cocci in clusters, catalase (+).

Causes what diseases?

A 
Food poisoning- heat stable enterotoxin
Toxic Shock syndrome- a super Ag
Scalded skin syndrome- exfoliative toxin
MRSA (Beta-lactam resist)
Acute nacteria; endocarditis
Osteomyelitis
Pneumonia (nosocomial, post-viral)
Surgical infection (MCC)
Bone pain + fever in kid (unless Sickle)
Impetigo
53
Q

S. aureus as normal flora and how transmitted?

A

Nares & skin

touching, sneezing, nose-picking, surgical wounds, food (custards, potato salad, canned meat)

54
Q

Predisposing factors for S. aureus infection

A

Surgery/wounds. Tampons, CGD, CF

55
Q

How does Toxic shock syndrome present? Mechanism

A

Mechanism: TSST (a super-Ag) binds to MHCII & TCR–> polyclonal Tcell activation

Sx: Fever, shock, desquamation, rash, vomit, end-organ failure

56
Q

Explain skin infections by S.aureus

A

Exfoliative toxin- cause Scalded skin syndrome & Bullou Impetigo

57
Q

Which GPC, catalase pos bug infects IV catheters and how?

A

Staph epidermidis via biofilms

58
Q

Strep pneumo MCC of what?

Gram stain look?

A

Meningitis (6months and older, even old)
Otitis media (kids)
Pneumonia- rusty colored sputum
Sinusitis

Gram stain: lancet shaped, GP diplo (“halo” sometimes, due to capsule)

59
Q

Draw GP flowchart. Include cocci, Rods, and branching bugs

A

pg 127

60
Q

What predisposes to Strep pneumo infection?

A 
influenza or measles infection
COPD
CHF
Asplenia and/or HgbS--> septicemia
Alcoholics (dont confuse w/ Klebsiella, which in this group)
61
Q

Which bugs are alpha hemolytic? How to differentiate among them?

A

Viridans strep & Strep pneumo

Optichin disk: O VR PS

62
Q

Transmission of GPC, catalase neg, Optochin resistant

A

normal flora in Oropharynx

63
Q

Viridinas strep diseases and causes

A

Dental caries & plaque- Strep mutans (Dextrans..)
Subacute bacterial endocarditis @ damaged valve plus dental work w/o antibiotics- S. sanguis

Fibrin/PLT bind to damaged site, and Viridans binds to fibrin via Dextrans polysach

64
Q

Subacutre endocarditis in colon cancer patient, whats da bug?

A

Streptococcus bovis

65
Q

Disease of GAS

A

Pyogenic: phayngitis, cellulitis, impetigo (honey-crusted lesions)
Toxigenic- scarlet fever, necrotizing fasciitis, TS-like syndrome
Immunologic- rheumatic fever, acute glomerulonephritis

66
Q

How to detect GAS, other than gram stain?

A

ASO titer
Bacitracin sensitive
PYR positive

67
Q

JONES criteria, use and define

A 
Diagnose Rheumatic fever (Type 2 HS)
Joints- polyarthritis
O- carditis
Nodules- subcutaneous
Erythema marginatum
Syndenham chorea (involuntary limb movement)
68
Q

What diseases caused following a Strep pyogenes infection (sequelae infections)

A

Phayngitis can cause rheumatic fever and acute glomerulonephritis

RF (HS 2): 2 wks after, Abs attack heart (molecular mimicry)
AGN (HS 3): Due to M-protein. Also after skin infection

69
Q

Sx of Scarlet fever? Associated bug?

A

Sx: scarlet rash (sparing face). strawberry/scarlet tongue, scarlet throat. Sandpaper rash (spares hands & soles), desquamation of hands soles

GAS

70
Q

How does Strep pyogenes spread?

A

Streptokinase, Streptococal DNAse, Hyaluronidase

71
Q

Diseases of GBS?
Prophylaxis?
Tx?

A

Sepsis, pneomonia, &
MCC of Neonatal meningitis:
Screen women 35-37wks pregnancy. If +, give intrapartum penicillin or ampicillin
(Clindamycin or erythromycin in allergies)

Tx: Ampicillin w/ aminoglycoside or cephalosporin

72
Q

Lab testing of GBS

A

CAMP factor, enlarging hemolysis area by S. aureus
Bacitracin resistant
Beta hemolytic
Hippurate positive

73
Q

Lab presentation of Enterococci

A

Lancefield group D
Variable hemolytic patterns
Growth on 6.5% NaCl & bile

74
Q

Diseases of Group D Strep

Examples of bugs

A

Penicillin G resistant cause UTI,
biliary tract infection,
subacute endocarditis- from procedures, (cystoscopy), from colon, perenium, genitals

Enterococcus faecalis & E. faecium

USMLE/ Step ONE (11 decks)

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