MI: Mycobacterial Diseases Flashcards
How can mycobacteria be categorised?
Rapid-growing and slow-growing
List three types of mycobacterial complex.
Mycobacterium tuberculosis complex
- Mycobacterium tuberculosis
- Mycobacterium bovis
Mycobacterium avium complex
- Mycobacterium avium
- Mycobacterium intracellulare
Mycobacterium abscessus complex
- Mycobacterium abscessus
- Mycobacterium massiliense
- Mycobacterium bolletii
Describe the morphology of mycobacteria.
- Non-motile rod-shaped bacteria
- Relatively slow-growing
- Cell wall composed of mycolic acids, complex waxes and glycoproteins
- Acid-alcohol fast
What is used as a screening test for mycobacterial infections?
Auramine stain
How are non-tuberculous mycobacterial infections transmitted?
- NOT person-to-person
- From the environment
- May be colonising rather than infecting
List three examples of slow-growing non-tuberculous mycobacteria and the diseases that they cause.
Mycobacterium avium intracellulare
- May invade bronchial tree or pre-existing bronchiectasis/cavaties
- Disseminated infection in immunocompromised patients
Mycobacterium marinum
- Swimming pool granuloma
Mycobacterium ulcerans
- Skin lesions (e.g. Bairnsdale ulcer, Buruli ulcer)
- Chronic progressive painless ulcer
List three examples of rapid-growing non-tuberculous mycobacteria.
- Mycobacterium abscessus
- Mycobacterium chelonae
- Mycobacterium fortuitum
List some risk factors for NTM.
Age
Underlying lung disease
How is Mycobacterium avium intracellulare treated?
- Clarthromycin/azithromycin
- Rifampicin
- Ethambutol
- +/- streptomycin/amikacin
What are the two types of Mycobacterium leprae infection?
- Paucibacillary tuberculoid - few skin lesions, robust T cell response
- Multibacillary lepromatous - multiple skin lesions, poor T cell response
What is the most common cause of death by infectious agent in the world?
- 1 = HIV
- 2 = TB
How many species are part of the Mycobacterium tuberculosis complex?
7 (including Mycobacterium tuberculosis, bovix and africanum)
What is the generation time of Mycobacterium tuberculosis?
15-20 hours
What is the infectious dose of Mycobacterium tuberculosis?
1-10 bacilli
Describe the natural history of primary TB.
- Usually asymptomatic
- Ghon focus (granuloma in the lungs)
- Controlled by cell-mediated immunity
- Occasionally causes diseeminated/military TB
What is post-primary TB?
Reactivation or exogenous re-infection
Happens > 5 years after primary infection
List some risk factors for reactivation of TB.
- Immunosuppression
- Chronic alcohol excess
- Malnutrition
- Ageing
List some types of extra-pulmonary TB.
- Lymphadenitis (scrofula) - cervical lymph nodes most commonly
- Gastrointestinal - due to swallowing of tubercle
- Peritoneal - ascitic or adhesive
- Genitourinary
- Bone and joint - due to haematogenous spread (e.g. Pott’s disease)
- Miliary TB
- Tuberculous meningitis
Why is it important to take 3 sputum samples when investigating suspected TB?
Increases the sensitivity of the smear microscopy
What investigation may be done in children with suspected TB?
Gastric aspirate
What is the turnaround time for smear microscopy and PCR?
2 hours
What is the issue with culturing TB?
It takes up to 6 weeks
What is the histological hallmark of TB?
Caseating granulomas
What is NAAT and why is it useful?
- Nucleic acid amplification test
- Allows speciation and the detection of drug resistance mutations
- Rapid
