Mycobacteria Flashcards
4 characteristics of the Mycobacterium genus
1) obligate aerobes
2) facultatively intracellular
3) rod-shaped
4) mycolic acid-rich cell walls, trait shared with fungi (results in acid fast staining)
3 typical & 3 atypical strains of Mycobacteria to know
typical: M. tuberculosis (Mtb), bovis, leprae
atypical: avium-intracellulare (MAC), kansasii, scrofulaceum
Mtb- natural habitat? how does infection occur? at-risk populations?
Humans = only natural reservoir;
Contamination = via large respiratory droplets (»sneezing), usu need to be within 3-6 ft, but more contagious from coughing in people with cavitary lesions
Popln: young, old, i-comp
Pathogenesis of primary Mtb
Inhalation -> alveolar macrophages consume the bacteria, which causes an interleukin 1/6/12/18 (inflamm) + interferon-gamma (CD4CD8 bacterial killing) + TNFalpha (inflamm) response=> granuloma grows (Ghon focus) to wall off the infection
Ghon focus vs Ghon complex
In Mtb:
Ghon focus: granuloma, usually mid/lower lobe fissure, that walls off the infection
Ghon complex: Ghon focus with the infection of the hilar lymphatics
Non-specific Mtb symptoms
Fever, weight loss, night sweats, malaise, hemoptysis
Active Mtb symptoms (primary) seen on CXR
pneumonitis, hilar lymphadenopathy
S/S of secondary Mtb- when does it occur?
Reinfection (months-decades after primary), typically in i-comp patients.
Upper lobe cavitary lesions, possibly miliary spread (tiny granulomas throughout lungs), produces more hemoptysis + non-specific symptoms.
How is Mtb diagnosed?
Acid-fast stained rods from sputum or biopsy.
3-6 weeks cultures grown on L-J media.
Extrapulmonary Mtb- pathogenesis? S/S?
Bacilli spread through blood/lymphatics to the LN, pleura, GI, CNS, and kidney. Kidney = most common site.
Non-specific symptoms + cutaneous lesions, enlarged viscera, organ dysfunction.
What’s the acid fast stain?
Picks up mycolic acid in cell walls
