Microbiology 9: Mycobacterial Disease Flashcards
What % of the world’s population are infected with TB?
About 33% (1.8bn) of the world’s population is infected with TB
How are mycobacteria classified?
Mycobacteria are divided into slow-growing and rapid-growing mycobacteria
- <7 days = rapid grower
- >7 days = slow grower
Which mycobacteria form the Mycobacterium Tuberculosis Complex?
- Mycobacterium tuberculosis*
- Mycobacterium bovis (BCG)*
Which mycobacteria form the Mycobacterium Avium Complex?
- Mycobacterium avium*
- Mycobacterium intracellulare*
Which mycobacteria form the Mycobacterium Abscessus Complex?
- Mycobacterium abscessus*
- Mycobacterium massiliense*
- Mycobacterium bolletii*
What is the structure of mycobacterium?
- 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)
Which stains are used for mycobacterium?
What are the features of Non-tuberculous Mycobacterium [NTB]?
Name some slow growing non-tuberculous mycobacterium (and give their features)
Name some rapid growing non-tuberculous mycobacterium (and give their features)
Give the epidemiology of non-tuberculous mycobacterium
- Ontario (MAC incidence high)
- Netherlands (incidence NTM increasing over MTB)
What are the risk factors for non-tuberculous mycobacterium?
- Age
- Underlying lung diseas
Which guidelines are used to diagnose non-tubercolous mycobacterium?
- BTS Guidelines 2017
- American Thoracic Society Guidelines
- Combines clinical findings with microbiology findings (blood culture, bronchoalveolar lavage, biopsy)
- Exclude other diagnoses
What is the Tx for non-tuberculous mycobacterium?
What are the 2 main types of Mycobacterium leprae?
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
What are the 2 main types of Mycobacterium leprae?
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
Describe the infection caused bu
- Multisystem disease
- Obligate aerobe [cannot survive without O2]
- Generation time 15-20hrs
Summarise the epidemiology of Mycobacterium tuberculosis
- 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
What are the 3 stages of disease of TB?
- Infected
- Latently infected (10% → active)
- Not become infected at all
How many closely related species are there in the MTB complex? Which are the most important ones?
7 closely related species, 3 important ones
- Mycobacterium tuberculosis
- Mycobacterium bovis
- Mycobacterium africanum
What is the lifetime risk of developing active TB from latent?
10% lifetime risk
How is TB transmitted?
- 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
How can TB be prevented?
What is the natural history of TB infection?
What is Post-Primary TB?
= a reactivation or exogenous re-infection:
- Happens >5 years after initial infection
- 5-10% lifetime risk
What are the risk factors for Post-Primary TB?
- Immunosuppression
- Chronicalcoholexcess
- Malnutrition
- Ageing
What is the clinical presentation of Post-Primary TB?
- Pulmonary or extra-pulmonary
- Host immune response shapes the clinical outcome– see image
Summarise the different stages of TB infection and their clinical findings, etc
What can Pulmonary TB cause? Which lobes of the lung is Pulmonary TB usually found in?
- Causes caseating granulomata:
- Lung parenchyma
- Mediastinal lymph nodes
- Commonly found in the upper lobes
Describe Extra-pulmonary TB
What is the Clinical Approach to MTB?
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
What are the risk factors for MTB?
- Non-UK born
- Homeless
- Close contacts
- HIV or other immunocompromise
- Drug users
- Young adults
What is the presentation of MTB?
fever, WL, night sweats and…
- Pulmonary (cough, haemoptysis)
- Malaise
- Anorexia
What are the Ix for ?MTB?
Summarise the smear test for MTB
- Sputum (60% sensitivity, but increases with additional samples → hence, 3 samples) o Gastric aspirated in children
- Rapid
- Operator-dependent
What is the Tx of TB?
What are the side effects of TB Tx?
How is TB Tx adherence monitored?
- Direct observation therapy / DOTS
- Video observed therapy / VOTS
What are the types of resistance to TB treatment?
- 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…
When does risk of drug-resistant TB increase?
Is HIV and TB co-infection common?
yes
What are the diagnostic challenges of HIV and TB co-infection?
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
What are the Tx challenges of HIV and TB co-infection?
- Timing of treatment initiation
- Drug interactions
- Overlapping toxicity
- Duration of treatment (adherence)
- Healthcare resources
