Mycobacterium tuberculosis

  • Gram positive rod,acidfast,stains red on zeihl Neilson staining due to high mycolic acid.
  • Obligate aerobe,LJ medium for growth
  • Produces Niacin
  • Virulence factor:Cord factor allows growth in extended chains.
  • Causes Pulmonary TB,primary disease affects lung bases, reactivation disease occur in upper lobes.

Ghons complex seen on CXR is a granuloma with an adjacent calcified LN.

Mycobacterium Leprae

  • Acid fast bacillus, seen within foamy(lipid laden) macrophages on biopsy.
  • Obligate aerobe
  • Bacilli are seen in groups called globi-cigar bundle appearance
  • Virchows lepra cells-Large undifferentiated histiocytes,globi seen inside.
  • Bacilli cannot grow in culture, grows on armadillo footpads.
  • Lepromatous leprosy:Extensive tissue and nerve damage,poor CMI,bacilli multiply is peripheral N endings,fingers,earlobes(cooler sites)
  • Tuberculoid leprosy-Macular skin lesions,granuloma formation,less bacilli,good CMI.

DOC:Dapsone with rifampicin.

Atypical Mycobacteria(Runyon’s classification)

  1. Photochromogens-M.Kansasii,M.simiae,M.Asiaticum
  2. Scotochromogens-M.Scrofulaceum(Pigmented colonies,even in dark)
  3. Nonphotochromogens-M.intracelulare(a/w AIDS),M.avium,M.Xenopi(epididymitis)
  4. Rapid growers(grow within 7 days)-M.chelonei(porcine heart valves),M.fortuitum,M.szulgai(Subcutaneous bursitis)
  5. Skin pathogens-M.Ulcerans(Buruli ulcer),M.marinum(swimming pool granuloma)

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