Mycobacteria Flashcards
- 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/cavities
• 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
- How is Mycobacterium avium intracellulare treated?
Clarithromycin/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
- How many species are part of the Mycobacterium tuberculosis complex?
7 (including Mycobacterium tuberculosis, bovis and africanum)
- Describe the natural history of primary TB.
Usually asymptomatic
Ghon focus (granuloma in the lungs)
Controlled by cell-mediated immunity
Occasionally causes disseminated/military TB
- 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
- Which investigation may be done in children with suspected TB?
Gastric aspirate
- What is NAAT and why is it useful?
Nucleic acid amplification test
Allows speciation and the detection of drug resistance mutations
Rapid
- What is the tuberculin skin test?
A sample of tuberculin is injected intradermally and left for 48-72 hours to observe the response
- What are the disadvantages of the tuberculin skin test?
Cross-reacts with BCG
Cannot distinguish between active and latent TB
- What is an IGRA assay?
Detection of antigen-specific IFN-gamma production
Does NOT cross-react with BCG
However, it cannot distinguish between latent and active TB
List some side effects of TB drugs
a. Rifampicin Raised transaminases CYP450 induction Orange secretions b. Isoniazid Peripheral neuropathy (give with pyridoxine) Hepatotoxicity c. Pyrazinamide Hepatotoxicity joint swelling d. Ethambutol Visual disturbance
- What is multi-drug resistant TB?
Resistant to rifampicin and isoniazid
- What is extremely drug resistant TB?
Resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable
- What are the diagnostic challenges of HIV and TB coinfection?
Clinical presentation is less likely to be classical
Symptoms may be absent if CD4+ count is low
More likely to have extra-pulmonary manifestations
Tuberculin skin test more likely to give false-negative
Low sensitivity for IGRAs
- What are the treatment challenges of HIV and TB coinfection?
Timing of treatment
Drug interactions
Overlapping toxicities
Duration of treatment
