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.
BCG vaccine false positives
- Vaccination with BCG may cause a false positive reaction to a TB skin test. A positive reaction to a TB skin test may be due to the BCG vaccine itself or due to infection with TB bacteria. … TB blood tests are the preferred method of TB testing for people who have received the BCG vaccine.
- IGRA has fewer false positives for those who have received the BCG vaccine
Histological features of TB
Caseating granulomas with central necrosis
and
Langerhans Giant cells (characteristic of 2o tuberculosis as shown in picture)
Describe the course of a TB infection
