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Pulm > Micro - TB > Flashcards

Micro - TB Flashcards

1
Q

4 mycobacteria strains and their reservoirs

A
  1. M. bovis - cows
  2. M. avium - AIDS pts
  3. M. tuberculosis - humans
  4. M. leprae - humans?
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2
Q

Presentation of M. bovis

A

Extrapulmonary TB in someone exposed to unpasteurized milk

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3
Q

Presentation of M. avium

A

TB-like dz in AIDS pt

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4
Q

M. tuberculosis is the leading cause of:

A

Death by bacterial infectious disease

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5
Q

How many people affected by TB worldwide?

A

1/3 of population

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6
Q

White plague v. black plague

A

White plague - TB

Black plague - Yersinia pestis (subcutaneous hemorrhage)

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7
Q

MTB is (aerobic, anaerobic) (intracellular, extracellular) (shape)

A

Aerobic, facultative aerobe, large rod

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8
Q

Where do mycobacteria normally reside in body?

A

Dry, oily areas

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9
Q

Virulence factors of MTB

A
  1. Facultative intracellular parasite
  2. Obligate aerobe
  3. Peptidoglycan + lots of lipoproteins
  4. Binds to mannose, complement, and Fc receptors of macrophages
  5. Inhibit phagosome-lysosome fusion
  6. Decreased oxidative toxicity of macrophages
  7. Antigen 85
  8. Slow generating
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10
Q

How does being a facultative intracellular parasite contribute to MTB virulence?

A

Avoids Ab/complement toxicity

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11
Q

How does being an obligate aerobe contribute to MTB virulence?

A

Can live in upper lobes of lungs

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12
Q

How does having peptidoglycan + lots of lipoproteins contribute to MTB virulence?

A 
Antibiotic resistance
Resistance to complement lysis
Resistance to stains
Resistance to acid or base compounds
Can live in macrophages
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13
Q

How does binding to mannose, complement, and Fc receptors of macrophages contribute to MTB virulence?

A

Allows cell entry

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14
Q

What is antigen 85 and how does it contribute to MTB virulence?

A

Group of proteins secreted by MTB that bind fibronectin and wall off the bacteria from immune cells + facilitate tubercle formation

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15
Q

How does the slow generation of TB contribute to virulence of MTB?

A

Can grow under the radar of immune cells

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16
Q

Characteristic of MTB culture

A

Serpentine cord colonies due to cord factor

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17
Q

Only virulent strains of MTB produce:

A

Cord factor

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18
Q

Characteristic of MTB gram stain

A

Ghost cells - mycolic acid repels the stain, causing cleared areas that resemble empty cells/ghosts

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19
Q

Name of acid-fast technique? How does it work?

A

Ziehl-Neelsen stain

Stain with carbolfuschin (pink dye) then decolorized with acid; holds “fast” to the pink stain

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20
Q

3 lipid proteins of MTB cell wall

A
  1. Mycolic acid
  2. Wax D
  3. Cord factor
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21
Q

To which MTB lipoprotein does carbolfuschin bind?

A

Mycolic acid

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22
Q

What is the function of mycolic acid?

A

Reduces permeability of MTB to ROS of macrophages

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23
Q

What is the function of cord factor?

A

2 mycolic acids + disaccharide that allows parallel growth of MTB (serpentine colonies) and inhibits PMN migration and complement deposition

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24
Q

What is the function of wax D?

A

Part of lipid envelope; major component of Freund’s complete adjuvant (solution used to boost immunity)

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25
Q

TB infection vs. disease

A 
Infection = immune system controlling MTB
Disease = immune system unable to control MTB
26
Q

When is MTB contagious?

A

During disease!!

27
Q

How does immune system control MTB?

A

Surrounds tubercles with macrophages, forming a hard shell that keeps MTB from spreading

28
Q

1 predisposing factor for MTB

29
Q

___% of people exposed with TB get infected

___% of people infected with TB get disease

30
Q

___% of AIDS patients have TB

A

10% (400x general population)

31
Q

(T/F): Most people infected with TB progress through stage 5 of the disease

A

False - only 10% infected develop disease, and only a small % of those will progress to stage 5

32
Q

Stage 1

A

Inhaled MTB taken up by alveolar macrophages

33
Q

Most infective droplet nuclei?

A

5 micrometers

34
Q

Nuclei droplet contain ~ ___ TB

35
Q

What happens to large droplet nuclei?

A

Deposit in URT where they do not cause infection

36
Q

Stage 2

A

MTB replicates in alveolar macrophages but they’re inactive so they can’t kill MTB; additional inactive macrophages recruited; can spread to lymph nodes via macrophages

37
Q

Time course of stage 2

A

Begins 7-21 days after infection

38
Q

Stage 3

A

Cell-mediated response
T cells release IFy –> activate macrophages –> destroy TB –> macrophages release lytic factors that cause tissue damage and tubercle formation

39
Q

Time course of stage 3? Significance?

A

6-10 weeks post infection

This is when skin test will be +; must re-test pt 2 months later if skin test -

40
Q

What is a tubercle?

A

Caseating granuloma lined by macrophages; MTB can’t multiply within these granulomas due to low pH and anoxic environment but they persist there

41
Q

Stage 4

A

Inactivated macrophages recruited by MTB for replication –> tubercle grows –> can spread to bronchus or blood vessel –> miliary TB

42
Q

Two types of lesions in milliary TB

A
  1. Exudative - PMNs surround MTB and they replicate without restriction = soft tubercle
  2. Productive or granulomatous - host becomes hypersensitive to tuberculoproteins = hard tubercle
43
Q

Stage 5

A

Center of tubercle caseates/liquifies which is conducive to MTB growth –> MTB grows extracellularly –> invades bronchus –> bronchus necrosis –> cavity and spread of MTB

44
Q

Two routes cavity can take:

A
  1. Heals and undergoes calcified fibrosis –> Gohn complex

2. Small metastatic foci heal and undergo calcified fibrosis –> Simon foci

45
Q

How do Gohn complex/Simon foci lead to reactivation?

A

Contain viable MTB

46
Q

When is TB considered MDR TB?

A

Resistant to 2+ Abx

47
Q

Typical regimen for TB and duration of tx?

A

RIPE (rifampin, isoniazid, pyrazinamide, ethambutol)

6-9 months

48
Q

Who would you expect to see XDR TB in?

A

HIV
Foreign-born
Reactivation TB

49
Q

Ways to diagnose TB

A
  1. PPD skin test
  2. Acid-fast stain
  3. CXR
  4. Culture
50
Q

How does PPD skin test work?

A

Inject pt with purified protein derivative (PPD; usually tuberculin); if macrophages have been activated, you will get a red welt

51
Q

How long do you wait before reading TB skin test?

52
Q

What would you see on CXR of primary TB?

A

Pleural effusion of any lobe + lymphadenopathy

53
Q

What would you see on CXR of reactivated TB?

A

Consolidation in upper lobe only + cavitations

54
Q

What would you see on CXR of milliary TB?

A

Caseating granulomas

55
Q

What is difficult about culture of MTB from sputum?

A

Slow growing so takes up to 4 weeks for dx; Abx resistance testing can take additional time

56
Q

Why might someone born outside US have + PPD?

A

Vaccinated or exposed to TB

57
Q

Could someone have a true + PPD without having MTB?

A

Yes - could have another strain of mycobacterium

58
Q

Why must you never give only a single agent in tx of TB?

A

Development of resistance; must give at least 4

59
Q

Name of TB vaccine? Type?

A

BCG

Live attenuated M. bovis

60
Q

Why don’t we give BCG in US?

A
  1. Makes PPD ineffective
  2. Can’t circumvent disease reactivation
  3. It can’t prevent infection, only disease

Pulm (33 decks)

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