mycobacteria Flashcards
what kind of bacteria are mycobacteria
- can grow on artifical media
- have a cell wall
- single cells
- rods
- ziehl/neelsen acid fast positive
- mycobacteria
which mycobacteria are medically important
M.tuberculosis – tuberculosis
M.leprae – leprosy
M.avium – disseminated infection in AIDS, infections in patients with chronic lung disease
M.kansasii – chronic lung infection
M.marinum – fish tank granuloma
M.ulcerans – buruli ulcer
Rapidly growing mycobacteria – skin and soft tissue infections
what makes mycobacteria resistant to gram stain
the high lipid content with mycolic acids in the cell wall
what stain do you use for mycobacteria
Ziehl-Neelsen stain
describe the microbiology of mycobacteria
Aerobic, non-spore forming, non motile bacillus
describe the cell wall of mycobacteria
Cell wall contains high molecular weight lipids
- Weakly gram-positive or colourless
- Survive inside macrophages, even in low pH environment
give 3 characteristics of mycobacteria
Slow reproduction
Slow response to treatment
Slow growing
generation time for M tuberculosis
15-20h
vs. 1h for common bacterial pathogens
challenges with TB
mycobacterium tuberculosis has a thick lipid-rich cell wall
this makes immune cell killing and penetration of drugs challenging
3 characteristics of TB
gradual onset of disease
takes much longer to diagnose
takes longer to treat
3 types of TB
- primary TB
- latent TB
- pulmonary TB
describe primary TB
initial contact made by alveolar macrophages
bacilli taken in by lymphatics to hilar lymph nodes
describe latent TB
cell mediated immune response from T cells
primary infection contained but CMI persists
no clinical disease
detectable CMI to TB on tuberculin skin test
describe pulmonary TB
granulomas form around bacilli that have settled in apex
in apex of lung there is more air and less blood supply (fewer defending white cells to fight)
TB may spread in lung causing other legions
could occur immediately following primary infection or a month later after reactivation
where can TB spread beyond the lungs
TB meningitis
Miliary TB
Pleural TB
Bone and Joint TB
Genito urinary TB
how does TB infect us
aerosol transmission
primary TB in lung
latent TB can remain for decades
can spread beyond lungs
impact of granulaoma formation on mycobacteria
if the granuloma works - mycobacteria shut down metabolically in order to survive dormancy
but if fails eg in lung - this can result in the formation of a cavity full of live mycobacteria and eventual disseminated disease
what does our body do to protect us against TB
- primarily controlled by macrophages
- requires a CD4 T cell response to be controlled
- involves many cells of immunity - formation of granulomas
- granuloma stability controls reactivation of TB
what is Acid fast bacilli used for
stain used to identify organisms with wax-like, thick cell walls e.g. mycobacteria (resistant to gram stain)
describe nucleic acid detection
Nucleic acid amplification test using PCR
Sensitivity 88%, specificity 98%
Recommended for rapid diagnosis in TB endemic countries
resistance mechanisms for TB drugs
drug inactivation
drug titration
alteration of drug target
how do we study TB
- animal models are a way to understand complex immunology
- mouse not a natural host of TB
- fish have their own mycobacterial species that can be used to help investigate host directed therapies
are mycobacteria common causes of diseaee
yes - Mycobacteria are common causes of human disease causing major human illness such a tuberculosis and leprosy
why do mycobacteria have unqiue staining patterns
They have unique lipid rich cell walls which give them unique staining patterns
why are mycobacteria hard to culture
They are slow growing
describe immune responses for TB
The immune response requires cell mediated immunity but many of the features of disease are associated with an aberrant immune response