TB-> Mycobacteria!!! Microm442 Deck 18 Flashcards
the sole genus of the family mycobacteriaceae (red snappers)
mycobacterium
Includes many environmental organisms
Often found in water, soil, foodstuffs
Nontuberculous mycobacteria
- Pulmonary disease similar to TB
- Lymphadenitis
- Skin and soft tissue diseases
- Disseminated diseases
important determinant of disease presence
and severity for all of these.
Host susceptibility
Acid fastness
Neither gram-negative nor –positive, but staining is often weakly positive.
* Results from the unique cell wall structure, with 60% mycolic acids (waxy coats) and lipoarabinomannan
(LAM in your book, or arabinogalactan below)
* Resists destaining by acid or ethanol
* Renders mycobacterial cells very resistant to drying (likely aids transmission in droplets)
Acid fast staining
(Ziehl-Neelsen or Kinyoun Stain)
- Stain with carbol fuchsin
- Decolorize with acid
alcohol - Counterstain with
methylene blue
Slow-growing and difficult to culture (fastidious) Divided into:
Slow-growing (um, particularly slow-growing?)
* M. tuberculosis, M. leprae are examples
* Generation times often 40x E. coli
* Forms visible colonies >7 day
Fast-growing (um, relatively fast-growing?)
* M. abscessus spp., chelonae are examples
* Forms visible colonies or growth ≤ 7 days
- Carotenoids of various structures
- May be used to speciate clinical isolates (can also use PCR and
biochemical tests)
distinctive pigments
aerobic or not?
aerobic
nonmotile except
m. marinum
host genetics
thought to play important role in
susceptibility/manifestations -> Defects in innate immune receptor signaling, IFN-g pathways
- Difficult to culture in vitro
- Difficult to manipulate genetically
- Renders laboratory
study difficult - Hinders diagnosis
Slow mycobacterial growth make them difficult to treat
- May be less likely to respond to standard antibiotics
- Often grow to high densities before immunity develops
- Can develop resistance to single agents easily
Recent(ish) resurgence
- Poverty
- Crowding
- Malnutrition
- Africa, Asia
hardest-hit - Multidrug
resistance - HIV/AIDS
TB: Impact of HIV
TB disease burden is highest in areas with endemic
HIV
* HIV increases susceptibility to TB infection
* HIV thought to worsen TB outcomes by impacting T-
cell-mediated immunity
* AIDS also increases susceptibility to nontuberculous
mycobacteria (NTM), especially M. avium complex