Week 2: Mycobacteriology

Question 1

Mycobacteria pathogen type

Answer 1

Intracellular pathogens

Question 2

Mycobacteria capsule type?

Answer 2

• Lipid and polypeptide capsule
• not stained by Gram stain due to mycolic acid & lipids in cell wall
• Stain is resistant to decolorization by acids (acid fast)

Question 3

Mycobacteria stains

Answer 3

• Ziehl-Nielson
• Kinyon
• Fluorochrome

Question 4

Mycobacteria culture media

Answer 4

• Lowenstein-Jensen
• Middlebrook agar

Question 5

Mycobacteria gram stain

Answer 5

not stained by gram stain due to mycolic acid & lipids

Question 6

Mycobacteria growth speed

Answer 6

Slower growth than other bacteria

Question 7

Mycobacteria acid-fast meaning

Answer 7

not easily decolorized by acids (as when stained) —used especially of bacteria and tissues.

Stain is resistant to decolorization by acids (Acid-fast)

Question 8

Mycobacterium tuberculosis metabolism type

Answer 8

Obligate aerobe

Question 9

Mycobacterium tuberculosis unique characteristics

Answer 9

prevents the fusion of phagosome with lysosomes (can survive in macrophages)

Question 10

Mycobacterium tuberculosis culture time

Answer 10

~6 weeks

Question 11

Mycobacterium tuberculosis transmission mechanism

Answer 11

Inhaled aerosol

Question 12

Mycobacterium tuberculosis prevention

Answer 12

N95 mask

Airborn isolation

Question 13

Mycobacterium tuberculosis infection types

Answer 13

• Latent infection: diagnosis ppd or IGRA
• Active disease: smear & culture, TB cord factor; PCR

Question 14

Pertinent strains of mycobacterium

4 listed

Answer 14

• Mycobacterium tuberculosis
• Mycobacterium avium-intracellulare
• Mycobacterium scofulaceum
• Mycobacterium marinum

Question 15

Mycobacterium tuberculosis

Answer 15

Causes TB and is often resistant to multiple drugs

Question 16

Mycobacterium avium-intracellulare

Answer 16

• causes disseminated, non-TB disease in AIDS
• often resistant to multiple drugs\
• prophylaxis with azithromycin when CD4+ count < 50 cells/mm³

Question 17

Mycobacterium scrofulaceum causes

Answer 17

cervical lymphadenitis in children

Question 18

Mycobacterium marinum causes

Answer 18

hand-infection in aquarium handlers

Question 19

All mycobacteria are?

Answer 19

Acid-fast pink rods

Question 20

TB symptoms

Answer 20

• fever
• night sweats
• weight loss
• cough (nonproductive or productive)
• hemoptysis

Question 21

Virulence factors of mycobacterium

Answer 21

• cord factor creates a serpentine cord appearance in virulent M tuberculosis strains; activates macrophages (promoting granuloma formation) and induces the release of TNF-α
• Sulfatides (surface glycolipids) inhibit phagolysosomal fusion

Question 22

TB and PPD

Answer 22

PPD + if current infection or past exposure

PPD - if no infection and in sarcoidosis or HIV infection (especially with low CD4+ cell count)

Question 23

Fewer false positives of TB after BCG vaccination

Answer 23

Interferon-γ release assay (IGRA) has fewer false positives from BCG vaccination

Question 24

What is the BCG vaccine?

Answer 24

Bacillus Calmette–Guérin vaccine is a vaccine primarily used against tuberculosis. In countries where tuberculosis or leprosy is common, one dose is recommended in healthy babies as close to the time of birth as possible.

Question 25

BCG vaccine false positives

Answer 25

• Vaccination with BCG may cause a false positive reaction to a TB skin test. A positive reaction to a TB skin test may be due to the BCG vaccine itself or due to infection with TB bacteria. … TB blood tests are the preferred method of TB testing for people who have received the BCG vaccine.
• IGRA has fewer false positives for those who have received the BCG vaccine

Question 26

Histological features of TB

Answer 26

Caseating granulomas with central necrosis

and

Langerhans Giant cells (characteristic of 2^o tuberculosis as shown in picture)

Question 27

Describe the course of a TB infection