Master Of Medicine

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)