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4 - Y5 a Path lectures 2021/22 > Microbiology 9: Mycobacterial Disease > Flashcards

Microbiology 9: Mycobacterial Disease Flashcards

1
Q

What % of the world’s population are infected with TB?

A

About 33% (1.8bn) of the world’s population is infected with TB

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2
Q

How are mycobacteria classified?

A

Mycobacteria are divided into slow-growing and rapid-growing mycobacteria

  • <7 days = rapid grower
  • >7 days = slow grower
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3
Q

Which mycobacteria form the Mycobacterium Tuberculosis Complex?

A
  • Mycobacterium tuberculosis*
  • Mycobacterium bovis (BCG)*
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4
Q

Which mycobacteria form the Mycobacterium Avium Complex?

A
  • Mycobacterium avium*
  • Mycobacterium intracellulare*
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5
Q

Which mycobacteria form the Mycobacterium Abscessus Complex?

A
  • Mycobacterium abscessus*
  • Mycobacterium massiliense*
  • Mycobacterium bolletii*
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6
Q

What is the structure of mycobacterium?

A
  • Non-motile rod-shaped bacteria (structurally gram +ve)
  • Relatively slow growing compared to other bacteria
  • Long-chain fatty (mycolic) acids, complex waxes and glycoproteins in cell wall
    • Structural rigidity
    • Complete Freund’s adjuvant
    • Staining characteristics
  • Acid-alcohol fast bacilli (AAFBs)
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7
Q

Which stains are used for mycobacterium?

A
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8
Q

What are the features of Non-tuberculous Mycobacterium [NTB]?

A
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9
Q

Name some slow growing non-tuberculous mycobacterium (and give their features)

A
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10
Q

Name some rapid growing non-tuberculous mycobacterium (and give their features)

A
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11
Q

Give the epidemiology of non-tuberculous mycobacterium

A
  • Ontario (MAC incidence high)
  • Netherlands (incidence NTM increasing over MTB)
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12
Q

What are the risk factors for non-tuberculous mycobacterium?

A
  • Age
  • Underlying lung diseas
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13
Q

Which guidelines are used to diagnose non-tubercolous mycobacterium?

A
  • BTS Guidelines 2017
  • American Thoracic Society Guidelines
  • Combines clinical findings with microbiology findings (blood culture, bronchoalveolar lavage, biopsy)
  • Exclude other diagnoses
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14
Q

What is the Tx for non-tuberculous mycobacterium?

A
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15
Q

What are the 2 main types of Mycobacterium leprae?

A

Paucibacillary tuberculoid

  • Few skin lesions + less joint infiltration
  • Robust T cell response

Multibacillary lepromatous

  • Abundance of bacilli
  • Multiple skin lesions + joint infiltration o Poor T cell response
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16
Q

What are the 2 main types of Mycobacterium leprae?

A

Paucibacillary tuberculoid

  • Few skin lesions + less joint infiltration
  • Robust T cell response

Multibacillary lepromatous

  • Abundance of bacilli
  • Multiple skin lesions + joint infiltration o Poor T cell response
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17
Q

Describe the infection caused bu

A
  • Multisystem disease
  • Obligate aerobe [cannot survive without O2]
  • Generation time 15-20hrs
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18
Q

Summarise the epidemiology of Mycobacterium tuberculosis

A
  • 2nd most common cause of death by infectious agent (after HIV) → 2m/year
  • Increasing incidence since the 1980s
  • 9000 cases per year in the UK
19
Q

What are the 3 stages of disease of TB?

A
  1. Infected
  2. Latently infected (10% → active)
  3. Not become infected at all
20
Q

How many closely related species are there in the MTB complex? Which are the most important ones?

A

7 closely related species, 3 important ones

  • Mycobacterium tuberculosis
  • Mycobacterium bovis
  • Mycobacterium africanum
21
Q

What is the lifetime risk of developing active TB from latent?

A

10% lifetime risk

22
Q

How is TB transmitted?

A
  • Droplet/airborne, suspended in air
  • Reaches the lower airway macrophages
  • Infectious dose is 1-10 bacilli (3,000 bacilli in a cough or 5 minutes talking)
  • Air remains infectious for 30 mins
23
Q

How can TB be prevented?

A
24
Q

What is the natural history of TB infection?

A
25
Q

What is Post-Primary TB?

A

= a reactivation or exogenous re-infection:

  • Happens >5 years after initial infection
  • 5-10% lifetime risk
26
Q

What are the risk factors for Post-Primary TB?

A
  • Immunosuppression
  • Chronicalcoholexcess
  • Malnutrition
  • Ageing
27
Q

What is the clinical presentation of Post-Primary TB?

A
  • Pulmonary or extra-pulmonary
  • Host immune response shapes the clinical outcome– see image
28
Q

Summarise the different stages of TB infection and their clinical findings, etc

A
29
Q

What can Pulmonary TB cause? Which lobes of the lung is Pulmonary TB usually found in?

A
  • Causes caseating granulomata:
    • Lung parenchyma
    • Mediastinal lymph nodes
  • Commonly found in the upper lobes
30
Q

Describe Extra-pulmonary TB

A
31
Q

What is the Clinical Approach to MTB?

A

Index of suspicion (ethnicity, recent travel, contacts,

BCG vaccination, non-specific exam findings, etc.)

Suggestive symptoms (fever, WL, night sweats, >2 weeks)

Investigations

Treatment

Preventing onwards transmission

32
Q

What are the risk factors for MTB?

A
  • Non-UK born
  • Homeless
  • Close contacts
  • HIV or other immunocompromise
  • Drug users
  • Young adults
33
Q

What is the presentation of MTB?

A

fever, WL, night sweats and…

  • Pulmonary (cough, haemoptysis)
  • Malaise
  • Anorexia
34
Q

What are the Ix for ?MTB?

A
35
Q

Summarise the smear test for MTB

A
  • Sputum (60% sensitivity, but increases with additional samples → hence, 3 samples) o Gastric aspirated in children
  • Rapid
  • Operator-dependent
36
Q

What is the Tx of TB?

A
37
Q

What are the side effects of TB Tx?

A
38
Q

How is TB Tx adherence monitored?

A
  • Direct observation therapy / DOTS
  • Video observed therapy / VOTS
39
Q

What are the types of resistance to TB treatment?

A
  • Due to spontaneous mutation + inadequate treatment
  • They require a 4/5-drug regimen of longer duration (9-12m)
  • Quinolones + aminoglycosides + para-aminosalicylic acid (PAS) + cycloserine + ethionamide
  • Current WHO recommendations state that 7 drugs should be used for 9-12 months
  • Risks side effects for longer…
40
Q

When does risk of drug-resistant TB increase?

A
41
Q

Is HIV and TB co-infection common?

A

yes

42
Q

What are the diagnostic challenges of HIV and TB co-infection?

A

Clinical presentation is less likely to be classical with symptoms and signs absent if low CD4+

CXR may be normal (more likely to have extra-pulmonary manifestations)

Smear microscopy and culture is less sensitive

Tuberculin skin test is more likely to be negative

Low sensitivity of IGRAs

43
Q

What are the Tx challenges of HIV and TB co-infection?

A
  • Timing of treatment initiation
  • Drug interactions
  • Overlapping toxicity
  • Duration of treatment (adherence)
  • Healthcare resources

4 - Y5 a Path lectures 2021/22 (37 decks)

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