Microbiology 17 - Mycobacterial disease Flashcards by Adya Rao

How are mycobacteria classified?

Based on speed of growth
<7 days = fast
>7 days = slow

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Recall 2 examples of slow-growing mycobacteria

M bovis
M tuberculosis

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What is the key cell wall component of mycobacteria that makes them so different from other bacteria?

Long chain fatty (mycolic) acids

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Recall 2 stains that can be used to identify mycobacteria

Auramine - operator dependent
Ziehl Neelsen

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In which patient group is M. avium complex most common?

HIV positive

**resembles TB infection if underlying lung disease

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Which type of mycobacterium is associated with cardiothoracic procedures?

M. chimera

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Which mycobactrium species is known as the “swimming poool granuloma”?

M. marinum

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How can M. marinum infection present?

Skin lesions on hands and arms of fish-owners

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What is the main symptoms of M. ulcerans infection?

Painless nodules >> destructive ulceration >> scarring + contractures

causes Buruli ulcer

**buzzword- travel to australia**

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What type of infection do fast-growing mycobacteria tend to cause?

Skin and soft tissue infections

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How should rapid-growing mycobacteria be treated?

Macrolide + additional antibiotics based on susceptibility testing

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What are the two forms of leprosy?

paucibacillary leprosy - milder version
Multibacillary lepromatous
- very severe
- disseminated

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Recall some strategies for TB prevention

Contact tracing and treatment of index case
Screening of those considered at risk
Vaccination
Improvement of living conditions

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What is required for diagnosis of TB?

3 sputum samples - smear them and culture them, NAAT if possible

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What are the 2 possible tests for latent TB?

Mantoux test
IGRAS (detection of antigen-specific interferon gamma)

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What duration of treatment should be given in CNS TB?

12 months

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What is the standard treatment regimen for M. tuberculosis?

2/12 rifampicin, isonoazid, pyrizinamide and ethambutol

4/12 rifampicin and isoniazid

**so total 6 months

all 4 drugs for 2 months

first 2 drugs for 4 months

What are the main side effects of each of the drugs used to treat M tuberculosis?

Rifampicin: orange secretions
Isoniazid: peripheral neuropathy - isoN for neuropathy. givrn with vitami b6 to prevent
Pyrizinamide: hepatotoxicity, hyperurucaemia–>gout
Ethambutol: visual disturbance - e for eyes

How can multi-drug resistant TB be treated?

More than 18 months treatment with at least 5 drugs

Where does TB infection become latent?

Gohn focus/ granuloma (in the lungs)

What is the name for spinal TB?

Pott’s disease

Which patients cannot receive the BCG vaccine?

Immunosuppressed patients as it’s a live attenuated vaccine

What treatment is used as TB prophylaxis?

Isoniazid monotherapy

Give some classical features of Leprosy

Skin depigmentation
Nodules
Trophic ulcers
Nerve thickening - most disability is due to nerve damage

What is the cause of a Buruli ulcer and how does it present?

Mycobacterium ulcerans Painless nodules progressing to ulceration, scarring and contractures

Outline the outcomes of someone with TB infection exposure

\*\* TB rarely causes symptoms with primary infection, only if immunocompromised

Classic lesions of TB

caseating grnaulomas

RF for TB infection

travel (South Asia / Eastern Europe), HIV+, homeless, IVDU, contact

Presentation of TB in immunocompromised patient

* *Subacute meningitis:** headaches, personality change, meningism, confusion. Diagnose with LP (see meningitis section) § **Spinal (Pott’s disease):** back pain, discitis, vertebral destruction, iliopsoas abscess § **Milliary TB:** disseminated haematogenous spread (seen on CXR) § Also lymphadenitis, pericarditis, peritonitis, renal, testicular, liver T

Which area of the lung does TB affect?

Upper lobe- cavitation (post primary TB)

How many sputum samples are needed to diagnose TB?

MC&S results for TB sputum sample

Microscopy on Ziehl-Neelson stain; culture on **Lowenstein-Jensen medium for 6wks** (gold standard) --\> acid fast bacilli seen (red against blue background)

How long does TB culture take to come back?

6 weeks

Tuberculin skin test vs IGRA test

**Tuberculin skin tests (Mantoux/Heaf):** shows exposure (active/latent/ BCG) **o IGRA (Elispot/Quantiferon):** shows exposure (active/latent) – NOT BCG

What are some second line drugs for TB?

injectables (amikacin, kanamycin), quinolones, linezolid

What is the risk of latent TB reactivation in an immunocompotenet individual?

10%

What % of the world has latent TB infection?

30%

How can leprosy present?

Leprosy manifests in a number of different ways due to a range of factors, most important being host immunology and bacterial virulence/initial infectious load. At one end of the spectrum is disseminated lepromatous/ multibacillary leprosy; Where the host immune system cannot contain the bacteria and it becomes widely **_disseminated_** Causes peri**pheral nerve inflammation and damage**, as well as dermatological lesions including ***nodules, hypoesthetic patches and the development of 'leonine'-like facial appearance***. Nerve thickening may be felt on palpation, with the most commonly affected nerves being the u**lnar, median, radial cutaneous, greater auricular, common peroneal and posterior tibial nerves.** At the other end of the spectrum is tuberculoid/paucibacillary leprosy; Where the immune system is able to control the infection and a milder form of nerve damage and dermatological manifestations occur. The nerve damage in all forms can lead to contractures, ulceration and deformity in the long term.

Multi-drug resistant tuberculosis is resistant to: Rifampicin and isoniazid Rifampicin and ethambutol Rifampicin and pyrazinamide Isoniazid and ethambutol Isoniazid and pyrazinamide

Rifampicin and isoniazid