19 - Mycobacterial diseases Flashcards
Mycobacteria are
slender bacillus
different: unusual waxy cell wall with high lipid content and slow growing and different media req.
Mycobacteria and gram staining
poor uptake
gram +ve: ghost cells
Retain certain stainds without decolourisation
Acid fast bacilli (AFBs)
Ziehl Neelsen, phenol auramine stains
Diseases caused by mycobacterium
TB - M.TB, M.bovis
Leprosy - M.leprae
Atypical mycobacteria = M.avium complex, M.kansasii, M.marinum (fish tank granuloma)
M. TB
Global emergency
1/3 infected
2million deaths pa
Mainly affects Africans
M.TB - pathogenesis
Inhalation of infected resp. droplets
Usually pulm.disease (>50% of cases)
M.TB - 1° TB
1° acquisition
periphery of lung midzone most common site
inhaled bacilli phagocytosed by macrophages
hilar lymph nodes - “Ghon focus”
Intracellular multiplication
M.TB - body’s response
Granuloma
Cell-mediated immune response
Central area of epithelioid cells, giant cells
Surrounding lymphocytic cell infiltration
Central area caseous necrosis
Fibrosis/calcification of lesions
Bacilli slowly die / remain viable for 20 years
M.TB - clinical presentation
influenza-like
CXR
TB skin test conversion
reactivation TB
lowered immunity >50yo malnutrition -OHism debilitating illness HIV Silicosis, chronic renal failure, gastrectomy
Anti-TNFa blockade e.g. infliximab
reactivation TB - clinical presentation
coalescing tubercles, central caseous necrosis
cavitation with high organism load
lung apices have highest oxygen tension
chronic productive cough w/ haemotypsis
weight loss, fever, night sweats
Extra-pulmonary
disseminated (miliary TB)
very young/old; immunocompromised
TB meningitis - clinical presentation
Often insidious onset unidentified fever personality change focal neuro deficit: basilar inflammation mild headache / meningism
may lack constitutional quartet
constitutional quartet
fever, night sweats, anorexia, weight loss
TB - diagnosis
clinical CXR Histology skin testing blood testing - IFN-y
Microbiology
