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