Myco. TB

Question 1

Myco. TB is non-…, non-…., and non-…?

Answer 1

non-motile, non-sporing, non-capsulated

Question 2

Is TB gram positive or gram negative and why?

Answer 2

Gram positive: it has thick peptidoglycan in outer membrane

Question 3

What shape is TB?

Answer 3

rod shape

Question 4

Do TB need oxygen to survive or not? What specific name are they given?

Answer 4

TB require oxygen to survive and are called OBLIGATE AEROBES

Question 5

State the layers of TB membrane, starting from cell membrane (bottom)

Answer 5

cell membrane, 
thick peptidoglycan
arbinogalactan
mycolic acid
myoside

Question 6

What is a special function of the arbinogalactan found in the cell membrane?

Answer 6

it allows the bacterium to survive inside macrophages by preventing the fusion of lysosome and phagosome

Question 7

What is the function of the mycolic acid in TB membrane?

Answer 7

makes the cell wall less permeable to certain substances such as ANTIBIOTICS - make it difficult for antibiotics to penetrate the bacterial wall

Question 8

What staining is used for TB?

Answer 8

Gram staining - positive but not very strong

Zeel Niesen - red rods on blue cells due to acid fast

Question 9

TB is an acid fast bacterium, explain why?

Answer 9

Has wax-like, nearly impermeable cell walls; contain mycolic acid + large amounts of fatty acids, waxes + complex lipids

Question 10

What culture medium is used for TB?
At what temp. and pH?
How long is the growth rate?

Answer 10

Lowenstein Jensen
Petragnani
Finleisen

37 degrees
pH 6-6.8

4-6 weeks

Question 11

Do they form colonies? what shape and what do they look like?

Answer 11

Yes they form colonies, R-shape colonies and look like bread crumbs

Question 12

What is the generation time?

Answer 12

12-18h

Question 13

Does TB produce any endo/exo toxins?

Answer 13

NO

Question 14

State the virulence factors of TB

Answer 14

Capable to survive in macrophages due to arbinogalactan in the membrane (prevents the fusion of lysosome and phagosome)

Cord factor: mycoside - causes serpentine growth and inhibits leukocyte migration + disrupts mitochondrial respiration and oxidative phosphorylation

Question 15

How is TB transmitted?

Answer 15

Humans:
inhalation
drinking contaminated cattle milk (cattles: M.bovis)
through skin 
conjuctiva (eyes)

Question 16

Who is at high risk from TB?

Answer 16

Prisoners (congregated settings)
HIV P with weakened IS
P in poverty and homeless
Alcoholism + drug addicts
Steroid use

Question 17

Stages of TB/ clinical forms

Answer 17

1) Primary: cough/ blood in sputum/ weakness/ temp/ weight loss + TB in lungs
2) Secondary (reactivation) : affects upper part of lungs - extrapulmonar localisation = kidneys, BM, LN, brains, CNS, gut, sepsis

Question 18

What type of immunity takes place?

Answer 18

Cell mediated immunity = means no Ab are produced, cells like T cells - cytotoxic cells work together to kill the bacteria

Question 19

What is the microbiological diagnosis of TB? 3 steps involved

Answer 19

Specimens of TB taken: CF , blood, urine
following: Microscopy - Culture and Isolation - Identification

1) Microscopy: stains are used for the microscopy
- Ziehl Neelsen (acid fast reaction)
- Immunofluorescent assay (IFA)

2) Culture + Isolation:
- Lowenstein Jensen = egg containing medium for primary isolation of the TB
- Preliminary treatment = specimen is decontaminated from other microbes
- Culturing: incubate culture for 4-6 weeks

Question 20

What 2 immunological tests are used for TB? Describe each test

Answer 20

1) Mantoux Test = in vivo - “TB SKIN TEST”
- injecting 0.1ml into skin
- produces wheal 6mm-10mm in diameter
- read the diameter reaction after 48-72h
- measure diameter

POSITIVE TEST - diameter > 15mm

2) Interferon gamma = in vitro
- test to detect interferon gamma especially produced by sensitised with TB Ag blood lymphocytes

Question 21

Outline the prophylaxis for TB

Answer 21

• isolation of the sick
• specific type of prophylaxis
• antibacterial prophylaxis
• long term treatment

Question 22

What is the specific prophylaxis for TB?

Answer 22

-BCG vaccine (vaccine for TB and leprosy) - immunised at birth and 7yrs after again

Question 23

When is antibacterial prophylaxis used for TB?

Answer 23

for those ionised for contact persons

Question 24

What are the long term treatments for TB?

Answer 24

• RIFAMPIN = inhibits RNA synthesis
• Streptomycin = Antibiotic
• Isoniazid = inhibits cell wall synthesis
• Ethambutol = inhibits cell wall synthesis