3. Tuberculosis

Causative agents of human TB?

M. tuberculosis complex: M. tuberculosis, M. bovis, M. africanum

How is TB transmitted?

Airborne droplet nuclei M. bovis: unpasteurised milk

Primary vs secondary TB?

Primary: Ghon focus + hilar nodes, usually silent Secondary (reactivation): apical cavities, cough, haemoptysis

1. Specimen — pulmonary TB?

Sputum × 3, early morning (Children: gastric aspirate)

1. Specimen — extrapulmonary TB?

Urine, CSF, pleural fluid, lymph node / tissue biopsy

1. Specimen — why decontaminate sputum?

NaOH (Petroff / NALC-NaOH) kills other flora; mycobacteria survive

2. Microscopy — stain and appearance?

Ziehl–Neelsen: red, thin, slightly curved acid-fast rods on blue background Auramine fluorescence (screening)

2. Microscopy — why acid-fast?

Mycolic acids in the waxy, lipid-rich cell wall

3. Cultivation — media?

Löwenstein–Jensen (egg + malachite green) Liquid MGIT / Middlebrook

3. Cultivation — growth?

Obligate aerobe, very slow: 3–8 weeks Rough, dry, cream "cauliflower / breadcrumb" colonies

4. Identification — rapid molecular test?

Xpert MTB/RIF Ultra (detects TB + rifampicin resistance) Line-probe assays

4. Identification — biochemical?

Niacin + Heat-labile catalase

4. Identification — immune tests for infection?

Mantoux: PPD intracutaneous, read 48–72 h, ≥10 mm induration IGRA (QuantiFERON)

5. Treatment — standard regimen?

2 months HRZE + 4 months HR (isoniazid, rifampicin, pyrazinamide, ethambutol)

5. Treatment — MDR-TB?

Resistant to isoniazid + rifampicin BPaLM for 6 months (bedaquiline, pretomanid, linezolid, moxifloxacin)

Prophylaxis?

BCG: live attenuated, intracutaneous, at birth Revaccinate only Mantoux-negative child