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 (usually <5), robust T cell response, low number of bacteria in the body
- Multibacillary lepromatous - multiple skin lesions (usually >5), poor T cell response, high number of bacteria
What is the most common cause of death by infectious agent in the world?
- 1 = HIV
- 2 = TB (10% of world infected)
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
What are the 2 types of primary TB infection
- Latent TB
- Asymptomatic
- Not contagious
- Active primary TB
- Symptomatic
- Infectious
- Can cause progessive disseminated disease
What is post-primary (secondary) TB?
Reactivation or exogenous re-infection
10% chance 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 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
What are the screening tests for latent TB
Tuberculin skin test
Interferon gamma release assay
