Classification

• Alcohol acid-fast bacilli
• Would be gram positive if Gram stain could penetrate walls

1. Typical mycobacteria
   • Mycobacterium Tuberculosis
   • Mycobacterium leprae
2. Atypical mycobacteria
   Resistant to standard antituberculosis drugs, different culture characteristics from MTB (eg pigment production, different growth rate in culture)
   • Mycobacterium avium intracellulare: - infection in AIDS
   • Mycobacterium marinum: - swimming pool granuloma
   • Mycobacterium ulcerans: - causes Buruli ulcer
   • Mycobacterium kansasii: - chronic pulmonary infection

Mycobacterium Tuberculosis

Clinical classification

1. Primary TB: usually symptomless
   • Lung - primary focus is "Ghon focus" with involvement of lymphatics and enlargement of hilar lymph nodes. Ghon focus forms at periphery of lung in mid-zone on a chest X-ray
   • Tonsils with cervical lymph node involvement "scrofula"
   • Terminal ileum with mesenteric lymph node involvement "tabes mesenterica"
2. Post-primary TB: cough, fever, weight loss. Spread of infection limited by severe local response with cavitation and fibrosis
   • Haematogenous spread: miliary TB in many organs, TB meningitis, bone/joint TB, renal TB
   • Spread by rupture into air spaces - TB bronchopneumonia