Mycobacterium Flashcards
What are mycobacteria?
Bacilli
Obligate aerobes
Cell Wall: High lipid content, mycolic acids
What is in the mycobacteria cell wall?
Mycelia acids
Lipoarabinomannan
“waxy coat”
What other name can mycobacteria be referred to?
Acid Fast Bacilli (AFB)
- binds carbol fuchsin dye
- acid fastness = resistance to decolorization by acid
Mycobacterium tuberculosis complex
majority of TB cases in humans
- M. tuberculosis
- M. africanum
- M. bovis
- M. bovis bacille calmette-guerin
Mycobacterium bovis
most commonly found in cattle
- eating or drinking unpasteurized dairy products
- direct contact with wound (bison, elk, deer)
- can be transferred through respiratory (human - human)
Mycobacterium Bovis Bacille Calmette-Guerin
VACCINE for tuberculosis
- infants and small children in other countries
- cancer treatmemt?
Non tubercuolosis mycobacterium
Found in soil, food, water and animals AQUIRED BY INGESTION, ASPPIRATION, INOCCULATION Slow growers * Mycobacterium kansasii * Mycobacterium avium *Leading cause of NTM infections Rapid growers (3-5 days) Special growers (can't grow in culture) * Mycobacterium leprae
How is TB spread?
Aerosols without visible primary lesion
Where is TB housed in primary infection>
base of lung close to pleura
What is the MTB virulence?
The ability to withstand the oxidative burst in phagocytosis by macrophages. Survive and replicate in macrophages.
MTB triggers…
T helper cell response
delayed type hypersensitivity
Inflammation – GRANULOMATOUS
Caseous necrosis in center
** if successful the infection is arrested.
Granuloma?
Masses or immune cells that form at site of infection
Caseous necrosis
morphological changes indicative of cell death caused by progressive enzymatic degradation
*cellular outline lost and tissue appears crumbly
If TB infection is arrested then….
caseous material is resorbed and is followed by fibrosis and dystrophic calcification
Ghon Complex
characteristic gross appearance with primary tuberculosis in the lung - yellow tan granuloma
visualization on CXR months to years later
In 90% of individuals TB infection remains latent but can become reactivated
.
Latent TB infection
people who ar infected but not sick
- do not have symptoms
- CAN NO spread TB to others
TB reactivation - SECONDARY TB
Principally in the LUNG - upper lobes
- obligate anaerob
- cavitation in upper lobes
Highest risk 1-2 years following exposure
Clinical features of TB
Cough (chronic) Sputum -- tissue necrosis Dyspnea (SOB) -- pulmonary parenchyme Fever -- inflammation Weight loss -- inflammation Night sweats
Caviatated CXR
Milliary CXR – small seeds over entire chest X-ray
Risk factors
Close contacts Health care workers Congregate settings IV drug abusers **HIV** Recent immigrants to US
Type IV hypersensitivity
DELAYED type hypersensitivity
- takes 2-3 days to develop
- not antibody mediated
Mantoux tuberculin skin test (TST)
PPD - purified protein derivative
- injected into inner surface of forearm - pale elevation of skin
- skin test read 48 - 72 hrs after administration
- reaction measured in MM OF INDURATION
This test tells us if the patient has latent TB not active TB. Delayed hypersensitvity.
Induration of 5 or more mm
HIV
recent infection
organ transplants
immunosuppressed
induration of 10 mm or more
recent immigrants drug users high risk congregate settings mycobacteriology lab personell children <4 yrs old
