Mycobacteria Flashcards
Mycobacteria properties
Aerobic
Non-spore forming
Bacilli
Slowing grow in culture (1-8 weeks)
Cell walls contain mycolic acid (long chain fatty acids) which make them acid fast
~150 species
Biosafety level 3 because they stay in the air for a long time
Non-tuberculosis (atypical) Mycobacteria
Environmental Some are opportunistic pathogens Some have little clinical significance Some are rapid growers M. leprae causes leprosy
Tuberculosis complex species (7)
tuberculosis bovis africanum microti canetti caprae pinnipedii
Mycobacterium tuberculosis
Thin, straight or curved rods, obligate aerobes, no spores
Single, pairs or in masses
Cell wall has high lipid content (60%) mycolic acid
Cell wall not stained by gram staining
Stain w Ziehl-Neelsen or Kinyoun Staining
Appears red with blue background
Long generation time
Can remain dormant in cells
How can resistance from M. tuberculosis occur
Only though chromosomal mutation
They do not exchange information with other bacteria
Ghon focus
Granuloma formed at the primary infection site
Extrapulmonary TB locations
CNS (meningitis) Miliary Bone GI/GU Lymph node
Systemic miliary TB
Occurs when infective foci in the lungs seed or rupture into one of the branches of the pulmonary venous return to the heart
Organism subsequently disseminates via arterial circulation
Typically affects: liver, bone marrow, spleen, adrenals, meninges, kidneys, fallopian tubes, and epidydymis
Cording
Organisms remain attached in parallel bundles to form long intertwining cords or ropes
Disease process of TB is largely to… (3 things)
Survival and multiplication in macrophages
Delayed hypersensitivity reaction to tuberculo-proteins
Cell wall lipids (produce granulomatous lesion)
Tuberculin skin test
Test to determine previous exposure to Tuberculo-protein
Inject fluid into dermis, gets absorbed, 2/3 days later check for bump (> 10mm)
2 ways to get false positives from the Tuberculin skin test
Previous vaccination with BCG
Infection with strongly cross reacting non tuberculosis mycobacteria
4 ways to get a false negative from the Tuberculin skin test
Recent TB infection (test becomes positive 4-6 weeks after)
Overwhelming TB disease (ex: miliary)
Immunosuppression/anergy (ex: AIDS)
Incorrect method of TST administration
Interferon Gamma Release Assays
In-vitro blood tests of cell mediated immune response Cross reacts with less NTMs Not affected by BCG Generally similar sensitivity Only one visit needed More expensive
Diagnosis of Active TB (4)
Microscopic examination of sputum (acid fast staining), at least 3 specimens, at least 1 hour apart
Culture (most sensitive, specific, and gold standard)
PCR
Chest radiograph
TST or IGRA not recommended for diagnosis in adults
2 media used to culture TB
Solid media (Lowenstein Jensen media) Liquid media culture
Mycobacteria detected in direct smears of clinical material contaminated with normal flora must be treated first by…
Decontaminating agent (e.g. NaOH) Digestion with Mucolytic agents also used for sputum specimens to dissolve mucus (N-acetyl L- cysteine)
What does M. tuberculosis produce that others do not?
Niacin
4 first line drugs for TB
Isoniazid* (bactericidal - intra and extracellular organisms)
Rifampicin* (same as above)
Pyrazinamide (bactericidal - acts at acidic pH in cells only)
Ethambutol (bacteriostatic)
6 second line TB drugs
Para-Aminosalicylic acid Streptomycin Ethionamide Cycloserine F Fluoroquinolones Kanamycin etc
Treatment regimen
All four first line drugs for 2 months, then just isoniazid and rifampicin for 4 motnhs
Poly-resistant
Resistance to more than one drug, but not the combination of isoniazid and rifampicin
Multidrug resistant
Resistance to at least isoniazid and rifampicin
Extensively drug-resistant (XDR)
MDR plus resistance to fluoroquinolones and at least 1 of the 3 injectable drugs (amikacin, kanamycin, capreomycin)
Differences between atypical and typical mycobacteria
Atypical: colonial morphology niacin test negative relatively more resistant to anti-TB drugs diseases typically less invasive
Mycobacterium leprae
Causes leprosy (Hansen’s disease)
Control programs have lead to reduction
Long incubation period
Does not grow on artificial culture media
Nose shedding
Varied spectrum of disease (discolored patches of skin, growths (nodules) on the skin, painless ulcers, painless swellings, skin numbness)
Type of leprosy if you have a
- Good CMI response
- Poor CMI response
- Intermediate CMI response
- Tuberculoid leprosy: lesions have numerous lymphocytes with few organisms, peripheral nerve involvement
- Lepromatous leprosy: lesions have numerous bacillis, less nerve involvement
- Borderline leprosy: lesions in between 1 and 2
How do we diagnose leprosy?
Skin biopsy from earlobe
Use PCR because we cannot grow it in the lab
Special type of stain
Treatment for leprosy
Dapson
Rifampin
Clofazimin
