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22 Cards in this Set
- Front
- Back
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Are most mycobacterium pathogenic?
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No
Most are soil and water organism |
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What kind of bacteria are the pathogenic mycobacteria?
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Can be Env't: humans are the accidental host (ex: M. avium)
Can be obligate pathogens with no known env't reservoir (ex: M. leprae) -> doesn't matter if this bacteria doesn't have its own env't, because it needs a host. Leprae can only grow in a mammalian host, not in a TT or on agar) |
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Which mycobacterium group are more likely to be pathogenic?
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Slow growing mycobacteria
(Rapd growing mycobact rarely cause disease) |
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What are some non-tubercuous mycobacterium that cuase disease in humans?
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Mostly part of slow growing gp
-M. avium: disseminated disease in AIDS, LN disease in kids (Scrofula) -M. avium subsp paratuberculosis: postulated agent of Crohn's -M. leprae: leprosy -M. ulcerans: cause of Buruli ulcer (Bairnsdale ulcer) |
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What is the M. tuberculosis complex (MTC)?
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M. tb, M. bovis (cows), M. caprae (goats), M. microti, M. africanum
--> All these are known as their own species, but are really just subspecies They cause TB in mammalian hosts They have identical 16s rRNA seq >99% homology in other genes Each has its own host preference |
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What is TB infection?
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Carrier state
Not infectious Latent, because bacteria are latent bacterial replication = death Not infectious, tuberculin positive (Not necessarily microbiologically dormant) Bacterial SURVIVAL Get in, stay in |
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What is tuberculosis in its diseased state?
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Actively replicating bacteria
Contagious, culturally positive Comes out of the body by coughing If you are culture positive, you're positive Get out, Spread Bacterial PATHOGENESIS |
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What needs to be studied when looking at a M. tb infection?
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-Species
-Dose and site of infection -Immune statues of host -> Age -> Constitutive immunity (host genetics) -> Acquired immunity (HIV, vaccine, drugs) |
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What are the outcomes of TB exposure?
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1) Exposure, no infection
-Frequency: 2/3 TB contacts don't get infected -?Bacterial dead at contact ? 2) Exposure, infection, no disease -90% won't get disease if immune competent -10x more common than disease 3) Exposure, infection, disease, +/- death -Variable latent period -5% in 2 yrs, 5% in rest of life |
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Describe the pathogenesis of TB.
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-Aerosol travels to alveoli of lung
-M. tb engulfed in alveolar macs Options: kill bact on contact or permit bacterial infection |
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What happens if the bacteria survive?
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Tuberculin positive
Infected macrophages attract other cells to aggregate (granuloma) |
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How many receptors do TB have for macrophages?
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Multiple different ones
->want macrophages to take them up |
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What can the granuloma do?
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1- Fail to contain the bacteria
Spread of organism by lymphatics/blood Primary TB 2- May contain bacteria for some time (years), then allow release later -Reactivation of TB *Granuloma can keep the bacteria at bay or let it spread* |
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What is the value of the granuloma?
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Host: Contain infection
Pathogen survival: bring more cells to the bacteria (help bact survive longer) Pathogen transmission: cause tissue damage |
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What is M. tb's exit strategy?
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Need inflammation
Hijack immune system to allow bacteria to spread |
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How is M. tb transmitted?
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Bacteria induces immune-pathology in the lungs
Cause patient to cough Upon coughing, thousands of bacteria are expelled into the air |
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Where does infection start?
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In the lungs
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Where does infection spread?
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Anywhere in the body (15%)
-But, extrapulmonary TB generally not contagious -Dead-end for bacteria |
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What's the clinical value of primary TB and reactivation TB?
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Clinically usually not evident
Therapeutically irrelevant |
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What is the relationship between TB and AIDS?
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Infection rates high to both (especially sun-saharan africa)
Evil synergy: HIV infection accelerates progression of TB infection to disease and TB infection accelerates progression of HIV to AIDS Countries with least resources most affected |
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Does HIV accelerate TB spread?
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No
AIDS patients are victims of TB epidemic ->Manifestation of a problem -> just accelerated infection to disease |
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TB epidemiology
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Most TB from human-human transmission:
-Respiratory aerosols (rarely other sources (ex M. bovis from milk) 1/3 world's population carry M. tb, but not infectious 8-9 million new cases/year, contagious 1.7 million deaths/year 20%mortality rate ~7.2 million ppl infected |
