Mycobacteria

Question 1

Mycobacteria properties

Answer 1

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

Question 2

Non-tuberculosis (atypical) Mycobacteria

Answer 2

Environmental
Some are opportunistic pathogens
Some have little clinical significance
Some are rapid growers
M. leprae causes leprosy

Question 3

Tuberculosis complex species (7)

Answer 3

tuberculosis
bovis
africanum
microti
canetti
caprae
pinnipedii

Question 4

Mycobacterium tuberculosis

Answer 4

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

Question 5

How can resistance from M. tuberculosis occur

Answer 5

Only though chromosomal mutation

They do not exchange information with other bacteria

Question 6

Ghon focus

Answer 6

Granuloma formed at the primary infection site

Question 7

Extrapulmonary TB locations

Answer 7

CNS (meningitis)
Miliary
Bone
GI/GU
Lymph node

Question 8

Systemic miliary TB

Answer 8

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

Question 9

Cording

Answer 9

Organisms remain attached in parallel bundles to form long intertwining cords or ropes

Question 10

Disease process of TB is largely to… (3 things)

Answer 10

Survival and multiplication in macrophages
Delayed hypersensitivity reaction to tuberculo-proteins
Cell wall lipids (produce granulomatous lesion)

Question 11

Tuberculin skin test

Answer 11

Test to determine previous exposure to Tuberculo-protein

Inject fluid into dermis, gets absorbed, 2/3 days later check for bump (> 10mm)

Question 12

2 ways to get false positives from the Tuberculin skin test

Answer 12

Previous vaccination with BCG

Infection with strongly cross reacting non tuberculosis mycobacteria

Question 13

4 ways to get a false negative from the Tuberculin skin test

Answer 13

Recent TB infection (test becomes positive 4-6 weeks after)
Overwhelming TB disease (ex: miliary)
Immunosuppression/anergy (ex: AIDS)
Incorrect method of TST administration

Question 14

Interferon Gamma Release Assays

Answer 14

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

Question 15

Diagnosis of Active TB (4)

Answer 15

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

Question 16

2 media used to culture TB

Answer 16

Solid media (Lowenstein Jensen media)
Liquid media culture

Question 17

Mycobacteria detected in direct smears of clinical material contaminated with normal flora must be treated first by…

Answer 17

Decontaminating agent (e.g. NaOH)
Digestion with Mucolytic agents also used for sputum specimens to dissolve mucus (N-acetyl L- cysteine)

Question 18

What does M. tuberculosis produce that others do not?

Answer 18

Niacin

Question 19

4 first line drugs for TB

Answer 19

Isoniazid* (bactericidal - intra and extracellular organisms)
Rifampicin* (same as above)
Pyrazinamide (bactericidal - acts at acidic pH in cells only)
Ethambutol (bacteriostatic)

Question 20

6 second line TB drugs

Answer 20

Para-Aminosalicylic acid
Streptomycin
Ethionamide
Cycloserine F
Fluoroquinolones
Kanamycin
etc

Question 21

Treatment regimen

Answer 21

All four first line drugs for 2 months, then just isoniazid and rifampicin for 4 motnhs

Question 22

Poly-resistant

Answer 22

Resistance to more than one drug, but not the combination of isoniazid and rifampicin

Question 23

Multidrug resistant

Answer 23

Resistance to at least isoniazid and rifampicin

Question 24

Extensively drug-resistant (XDR)

Answer 24

MDR plus resistance to fluoroquinolones and at least 1 of the 3 injectable drugs (amikacin, kanamycin, capreomycin)

Question 25

Differences between atypical and typical mycobacteria

Answer 25

Atypical:
colonial morphology
niacin test negative
relatively more resistant to anti-TB drugs
diseases typically less invasive

Question 26

Mycobacterium leprae

Answer 26

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)

Question 27

Type of leprosy if you have a

1. Good CMI response
2. Poor CMI response
3. Intermediate CMI response

Answer 27

1. Tuberculoid leprosy: lesions have numerous lymphocytes with few organisms, peripheral nerve involvement
2. Lepromatous leprosy: lesions have numerous bacillis, less nerve involvement
3. Borderline leprosy: lesions in between 1 and 2

Question 28

How do we diagnose leprosy?

Answer 28

Skin biopsy from earlobe
Use PCR because we cannot grow it in the lab
Special type of stain

Question 29

Treatment for leprosy

Answer 29

Dapson
Rifampin
Clofazimin