Micro 9 - Mycobacterial disease

Question 1

Purpose of auramine + Ziehl Neelsen staining in mycobacteria

Answer 1

o Auramine = screening

o Ziehl-Neelsen = diagnosis

Question 2

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

Answer 2

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

Question 3

Give examples of rapid growin non tuberculous mycobacteria

Where are they implicated?

Answer 3

o Mycobacterium abscessus
o Mycobacterium chelonae
o Mycobacterium fortuitum

 Skin and soft tissue infections
 Tattoo-associated outbreaks
o CF and bronchiectasis

Question 4

Diagnosis of non tuberculous mycobacteria

Answer 4

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

Question 5

Slow growing NTM mx

Answer 5

RiCES

Rifampicin
Clarithromycin/ Azithromycin
Ethambutol
+/- streptomycin or amikacin

Question 6

2 main types of mycobacterium leprae + sx

Answer 6

• 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

Question 7

How high is the risk of developing active TB from latent infection

Answer 7

10%

Question 8

MTB complex

Answer 8

7 closely related species

M tuberculosis
M bovis
M africanum

Question 9

Which strain does the BCG (Bacille Clamette Guerin) vaccine contain

Answer 9

live attenuates strain of M bovis

Question 10

TB buzzwords

Answer 10

Gohn focus/ granuloma

Erythema nodosum

Question 11

 Pulmonary or extra-pulmonary

Answer 11

• 51.4% of cases in the UK are extra-pulmonary

localised extrapulmonary first, then as immune response become less effective -> localised pulmonary

Question 12

Sputum samples for ix of TB

How many
Stain
Culture

Answer 12

 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

Question 13

Role of NAAT for primary samples?

Answer 13

Rapid diagnosis of smear +ve

Drug resistance mutations

Question 14

Dx of active TB

Answer 14

culture and sensitivity

Question 15

Dx of latent/previous exposure to Mycobacteria TB

Answer 15

 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

Question 16

TB mx

Answer 16

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

Question 17

SE of TB mx

Answer 17

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

Question 18

TB prophylaxis

Answer 18

Isoniazid monotherapy

Question 19

Multidrug resistant TB (MDR) + Extremely dug resistant (XDR) TB definition

Answer 19

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

Question 20

MDR TB mx

Answer 20

 Current WHO recommendations state that 7 drugs should be used for 9-12 months

Question 21

o Risk of drug-resistant TB increases if:

Answer 21

 Previous TB treatment

 HIV+
 Known contact of MDR TB
 Failure to respond to conventional TB
 >4 months smear +ve or >5 months culture +ve

Question 22

Non-tuberculous Mycobacterium [NTM]

where are they found
sx

Answer 22

• 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)