Micro 9 - Mycobacterial disease Flashcards
Purpose of auramine + Ziehl Neelsen staining in mycobacteria
o Auramine = screening
o Ziehl-Neelsen = diagnosis
Buzzwords for slow growing non tuberculous mycobacteria
Disseminated infection in immunosuppressed
cardiothoracic procedures, infective endocarditis
Swimming pool granuloma /Aquarium owners/ Papules/plaques
painless nodule progressing to ulceration/ chronic progressive painless ulcer after travel to the tropics/ australia
Slow growing = >7 days
Disseminated infection in immunosuppressed –> Mycobacterium avium intracellulare (MAI/MAC)
cardiothoracic procedures, infective endocarditis - Mycobacterium chimera
Swimming pool granuloma /Aquarium owners/ Papules/plaques - Mycobacterium marinum
chronic progressive painless ulcer after travel to the tropics/ australia - mycobacterium ulcerans
Give examples of rapid growin non tuberculous mycobacteria
Where are they implicated?
o Mycobacterium abscessus
o Mycobacterium chelonae
o Mycobacterium fortuitum
Skin and soft tissue infections
Tattoo-associated outbreaks
o CF and bronchiectasis
Diagnosis of non tuberculous mycobacteria
Lung disease
Clinical: pulmonary symptoms, nodular/cavitary opacities, multifocal bronchiectasis with multiple small nodules
Exclusion of other diagnoses
Microbiologic:
Positive culture >1 sputum samples
OR +ve BAL
OR +ve biopsy with granulomata
Slow growing NTM mx
RiCES
Rifampicin
Clarithromycin/ Azithromycin
Ethambutol
+/- streptomycin or amikacin
2 main types of mycobacterium leprae + sx
• Paucibacillary tuberculoid
o Few skin lesions + less joint infiltration
o Robust T cell response
o Less aggressive
o Can convert to multibacillary lepromatous
• Multibacillary lepromatous o Abundance of bacilli o Multiple skin lesions + joint infiltration o Poor T cell response o More aggressive
- Skin depigmentation
- Nodules
- Trophic ulcers
- Nerve thickening
- Life-long illness
- Most disability due to nerve damage
How high is the risk of developing active TB from latent infection
10%
MTB complex
7 closely related species
M tuberculosis
M bovis
M africanum
Which strain does the BCG (Bacille Clamette Guerin) vaccine contain
live attenuates strain of M bovis
TB buzzwords
Gohn focus/ granuloma
Erythema nodosum
Pulmonary or extra-pulmonary
• 51.4% of cases in the UK are extra-pulmonary
localised extrapulmonary first, then as immune response become less effective -> localised pulmonary
Sputum samples for ix of TB
How many
Stain
Culture
Sputum x3
(gastric aspirates in kids)
Stain for acid fast bacilli on smear (non specific for all mycobacterium)
• Microscopy on Ziehl-Neelson stain
• Culture on Lowenstein-Jensen medium for 6 weeks – gold standard – acid fast bacilli seen - GOLD STANDARD
Role of NAAT for primary samples?
Rapid diagnosis of smear +ve
Drug resistance mutations
Dx of active TB
culture and sensitivity
Dx of latent/previous exposure to Mycobacteria TB
Tuberculin skin test (TST)
• Previous exposure to Mycobacteria (Mantoux/Heaf)
o Active/latent/BCG
o Cross-reacts with BCG – will be positive if person is vaccinated
• 2 units of tuberculin, intradermal, examine 48-72hrs later
• Delayed type hypersensitivity reaction (PPD = Purified Protein Derivative)
IGRA (IFNg release assay e.g. ELISpot, QuantiFERON)
• Detect antigen-specific IFNg production
o Active/latent/not BCG
o No cross-reaction with BCG (unlike in TST) - use this if prev. exposure (i.e. vaccination)
o Cannot distinguish latent and active TB
TB mx
o R Rifampicin 6m
o I Isoniazid 6m
o P Pyrazinamide 2m
o E Ethambutol 2m
Duration
o All 4 for 2 months
o Continue rifampicin + isoniazid for further 4 months
o Then rifampicin + Isoniazid for 4/12
SE of TB mx
o Rifampicin:
Orange secretions
Raised transaminases (ALT/AST)
Induces CYP450
o Isoniazid:
Peripheral neuropathy (give with pyridoxine (B6))
Hepatotoxicity (Drug-induced liver injury – DILI)
o Pyrazinamide:
Hepatotoxicity (DILI)
o Ethambutol:
Optic neuritis
TB prophylaxis
Isoniazid monotherapy
Multidrug resistant TB (MDR) + Extremely dug resistant (XDR) TB definition
o Multi-Drug Resistant (MDR) resistant to rifampicin and isoniazid
o Extremely Drug Resistant (XDR) resistant to rifampicin, isoniazid, fluoroquinolones and at least 1 injectable
MDR TB mx
Current WHO recommendations state that 7 drugs should be used for 9-12 months
o Risk of drug-resistant TB increases if:
Previous TB treatment
HIV+
Known contact of MDR TB
Failure to respond to conventional TB
>4 months smear +ve or >5 months culture +ve
Non-tuberculous Mycobacterium [NTM]
where are they found
sx
• Ubiquitous in nature
• Environmental – water and soils, can form a biofilm – if this happens foreign material needs to be removed
o Foreign materials, plastics e.g. catheters
- Atypical
- Varying spectrum of pathogenicity (majority are not pathogenic to humans)
- May be found colonising in humans (not infecting)
- Little risk of person-to-person
• Commonly resistant to the usual anti-TB therapy (use RiCE - Backbone of treatment is usually a macrolide)
