Week 2: Mycobacteriology Flashcards
Mycobacteria pathogen type
Intracellular pathogens
Mycobacteria capsule type?
- Lipid and polypeptide capsule
- not stained by Gram stain due to mycolic acid & lipids in cell wall
- Stain is resistant to decolorization by acids (acid fast)
Mycobacteria stains
- Ziehl-Nielson
- Kinyon
- Fluorochrome
Mycobacteria culture media
- Lowenstein-Jensen
- Middlebrook agar
Mycobacteria gram stain
not stained by gram stain due to mycolic acid & lipids
Mycobacteria growth speed
Slower growth than other bacteria
Mycobacteria acid-fast meaning
not easily decolorized by acids (as when stained) —used especially of bacteria and tissues.
Stain is resistant to decolorization by acids (Acid-fast)
Mycobacterium tuberculosis metabolism type
Obligate aerobe
Mycobacterium tuberculosis unique characteristics
prevents the fusion of phagosome with lysosomes (can survive in macrophages)
Mycobacterium tuberculosis culture time
~6 weeks
Mycobacterium tuberculosis transmission mechanism
Inhaled aerosol
Mycobacterium tuberculosis prevention
N95 mask
Airborn isolation
Mycobacterium tuberculosis infection types
- Latent infection: diagnosis ppd or IGRA
- Active disease: smear & culture, TB cord factor; PCR
Pertinent strains of mycobacterium
4 listed
- Mycobacterium tuberculosis
- Mycobacterium avium-intracellulare
- Mycobacterium scofulaceum
- Mycobacterium marinum
Mycobacterium tuberculosis
Causes TB and is often resistant to multiple drugs
Mycobacterium avium-intracellulare
- causes disseminated, non-TB disease in AIDS
- often resistant to multiple drugs\
- prophylaxis with azithromycin when CD4+ count < 50 cells/mm3
Mycobacterium scrofulaceum causes
cervical lymphadenitis in children
Mycobacterium marinum causes
hand-infection in aquarium handlers
All mycobacteria are?
Acid-fast pink rods
TB symptoms
- fever
- night sweats
- weight loss
- cough (nonproductive or productive)
- hemoptysis
Virulence factors of mycobacterium
- cord factor creates a serpentine cord appearance in virulent M tuberculosis strains; activates macrophages (promoting granuloma formation) and induces the release of TNF-α
- Sulfatides (surface glycolipids) inhibit phagolysosomal fusion
TB and PPD
PPD + if current infection or past exposure
PPD - if no infection and in sarcoidosis or HIV infection (especially with low CD4+ cell count)
Fewer false positives of TB after BCG vaccination
Interferon-γ release assay (IGRA) has fewer false positives from BCG vaccination
What is the BCG vaccine?
Bacillus Calmette–Guérin vaccine is a vaccine primarily used against tuberculosis. In countries where tuberculosis or leprosy is common, one dose is recommended in healthy babies as close to the time of birth as possible.
