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140 SEcTioN ii Microbiology ` microbiology—cliNical bacteriology Microbiology ` microbiology—cliNical bacteriology

Mycobacteria Gram ⊕ acid fast rods (pink rods, arrows in A ). TB symptoms include fever, night sweats,
A Mycobacterium tuberculosis (TB, often weight loss, cough (nonproductive or
resistant to multiple drugs). productive), hemoptysis.
M avium–intracellulare (causes disseminated, Cord factor creates a “serpentine cord”
non-TB disease in AIDS; often resistant appearance in virulent M tuberculosis strains;
to multiple drugs). Prophylaxis with activates macrophages (promoting granuloma
azithromycin when CD4+ count < 50 cells/ formation) and induces release of TNF-α.
3
mm . Sulfatides (surface glycolipids) inhibit
M scrofulaceum (cervical lymphadenitis in phagolysosomal fusion.
children).
M marinum (hand infection in aquarium
handlers).

Tuberculosis
Mycobacterium Interferon-γ release assay (IGRA) has fewer
tuberculosis false positives from BCG vaccination.
Hilar nodes
+ PPD ⊕ if current infection or past exposure.
Ghon
complex Ghon focus PPD ⊝ if no infection and in sarcoidosis or
(usually mid/ HIV infection (especially with low CD4+ cell
lower lobes)
Primary tuberculosis count).
> 90% < 10% Caseating granulomas with central necrosis
Healing by fibrosis Progressive primary tuberculosis and Langhans giant cell (single example
Calcification (AIDS, malnutrition) in A ) are characteristic of 2° tuberculosis.
(PPD )
Reactivation Progressive A
lung disease
2° tuberculosis
Bacteremia
Fibrocaseous
cavitary lesion
(usually upper Meninges
lobes) Miliary
tuberculosis
Vertebrae
(Pott disease)
Localized destructive disease Lymph nodes
Cavity
Caseation Caseation Lungs Spleen
Scar
Liver Adrenal
gland
Joints and
long bones

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