Microbiology 17 - Mycobacterial disease Flashcards
(30 cards)
How are mycobacteria classified?
Based on speed of growth
<7 days = fast
>7 days = slow
Recall 2 examples of slow-growing mycobacteria
M bovis
M tuberculosis
M avium and intracellulare
What is the key cell wall component of mycobacteria that makes them so different from other bacteria?
Long chain fatty (mycolic) acids
complex waxes and glycoproteins in cell wall
Structural rigidity
Recall 2 stains that can be used to identify mycobacteria
acid alcohol fast bacilli (AAFBs)
Auramine (fluorescent) = screening
Ziehl-Neelsen = diagnosis
In which patient group is M. avium complex most common?
HIV positive
causes disseminated infection in immunosuppressed
Which type of mycobacterium is associated with cardiothoracic procedures?
M. chimera
Which mycobactrium species is known as the “swimming poool granuloma”?
M. marinum
How can M. marinum infection present?
Skin lesions on hands and arms of fish-owners
What is the main symptoms of M. ulcerans infection?
Skin lesions (e.g. Bairnsdale ulcer, Buruli ulcer)
Chronic progressive painless ulcer
What are some examples of fast growing NTM?
Mycobacterium abscessus
Mycobacterium chelonae
Mycobacterium fortuitum
What type of infection do fast-growing mycobacteria tend to cause?
Skin and soft tissue infections
Tattoo associated outbreaks
Hospital settings from blood cultures (i.e. when vascular catheters are being used; plastic surgery)
How should MAC/slow growing NTM be treated?
Rifampicin
Clarithromycin/azithromycin
Ethambutol
+/- streptomycin/Amikacin
RiCES
How should rapid-growing mycobacteria be treated?
Macrolide + additional antibiotics based on susceptibility testing
What is the most severe form of disease that mycobacterium leprae can cause?
Multibacillary lepromatous
Abundance of bacilli
Multiple skin lesions + joint infiltration
Poor T cell response
(Paucillary tuberculoid would cause few skin lesions, less joint infiltration and robust T cell response)
Is TB an aerobe or anaerobe?
Obligate aerobe [cannot survive without O2]
what are some extra-pulmonary features of TB?
Lymphadenitis (AKA: scrofula) – some children react to BCG with this…
Gastrointestinal - like IBD – do NOT treat with infliximab!
Bone and Joint - Haematogenous spread, Spine (Pott’s disease)
Miliary TB - Millet seeds on CXR
Tuberculous meningitis
What is required for diagnosis of TB?
3 sputum (gastric aspirates in children) sample cultures
- AAFB (non-specific for all mycobacterium)
- BAL → culture (gold-standard, 6w) on Lowenstein-Jenson medium → stain auramine, Ziehl-Neelson
- NAAT (nucleic acid amplification test) → diagnose smear +ve sample, rapid, also identifes resistance
- Histology – e. caseating granuloma
What are the 2 possible tests for latent TB?
Tuberculin skin test (TST) i.e. Manteaux
Delayed type hypersensitivity reaction
Cross reacts with BCG (finds vaccination, latent or active – no differentiation)
IGRA (IFNg release assay) – detect antigen-specific IFNg production:
Examples: ELISpot and QuantiFERON
No cross-reaction with BCG (unlike in TST) use this if prev. exposure (i.e. vaccination)
Cannot distinguish latent and active TB
Issues with sensitivity and specificity
What are some radiological findings in TB?
CXR and other radiology (miliary/beads TB, mediastinal lymphadenoapthy, predilection to apices, etc.)
What duration of treatment should be given in CNS TB?
12 months
What is the standard treatment regimen for M. tuberculosis?
2/12 rifampicin, isonoazid, pyrizinamide and ethambutol (RIPE)
4/12 rifampicin and isoniazid (RI)
What are the main side effects of each of the drugs used to treat M tuberculosis?
Rifampicin: orange secretions (Raised transaminases (ALT/AST) Induces CYP450)
Isoniazid: peripheral neuropathy (give w/ pyroxidine) , Hepatotoxicity (DILI)
Pyrizinamide: hepatotoxicity
Ethambutol: visual disturbance
How can multi-drug resistant TB be treated?
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…
What is MDR TB?
resistance to rifampicin and isoniazid
extremely drug resistant (XDR) → also to fluoroquinolones and a least 1 injectable
