Mycobacteria

Question 1

Which species of mycobacteria cause tuberculosis? (5-10)

Answer 1

M. tuberculosis
M. bovis & M. bovis BGC
M. africanum
M. pinnipedii
M. microti
M. caprae
M. canettii
M. orygis
M. suricattae
M. mungi

Question 2

How is tuberculosis transmitted?

Answer 2

Droplets (except M. bovis via infected milk)

Question 3

What is a tubercule?

Answer 3

small knoblike that project from surface

Question 4

Name two staining methods for visualising mycobacteria under the light microscope.

Answer 4

Zeihl neelsen

Kinyoun stain

Question 5

Why are mycobacteria slow growing?

Answer 5

bc of hydropobic cell wall = slow uptake of nutrients

Question 6

What makes them so resistant to acids, alkalis and desiccation?

Answer 6

Cell wall: high lipid, phospholipid, hydrophobic

Question 7

What is cording? Which organism(s) produce cording?

Answer 7

AFB (TB strains) clump together bc of hydrophobic cell wall

Question 8

What can you say about the sensitivity and specificity of seeing cording in a blood culture bottle?

Answer 8

Sens: 89.2% (not all TB strains clumped)
Spec: 99.2% (all strains that clumped were TB)

Question 9

List the 5 groups of NTM (non-tuberculosis mycobacteria). What are the growth characteristics that categorise each group of the NTM?

Answer 9

• 1-3: Slow* growers (>7 days to appear on media)*
  1: Photochromogens (light = pigment)
  2: Scotochromogen (light + dark = pigment)
  3. Non-photochromagens (no pigment)
  4: Rapid* growers (<7 days & usually no pigments)
  5: Non-cultivatable* (M.leprae)

Question 10

How is leprosy diagnosed? What is the disease’s common name?

Answer 10

a) Skin biopsy for AFB* (M. leprae), PCR if Hi # (CAN”T be grown on media)
b) Hansen’s disease

Question 11

How frequently is leprosy diagnosed in Australia?

Answer 11

Rare

Question 12

Describe the pathogenesis of tuberculosis (process it infects host).

Answer 12

1. Transmission by droplets (/infected milk)
2. Enter body => cause DISEASE OR DORMANT (inactive initially or even after treatment)
3. Pulmonary disease common but may spread systemically (e.g. kidneys)
4. immune rxn to TB => tissue damage w/ involvement of humoural & cell mediated resp

Question 13

What treatment options are there for patients infected with the resistant Indian strain(s) of TB?

Answer 13

untreatable? link in slide 43*****

Question 14

If a clinical request for a wound swab stated that the patient was a fisherman, which species of Mycobacterium might be expected from this site?

Answer 14

Mycobacteria marinum

Question 15

Explain why PCR is not necessarily a reliable means for detecting the presence of tuberculosis causing mycobacteria?

Answer 15

PCR not sensitive w/ low No. organisms

Question 16

how is M. leprae transmitted>

Answer 16

1. prolonged contact of exudate or abraded skin of infected ppl
2. inhalation of aerosols

Question 17

90% of mycobacterium infection is caused by

Answer 17

M.avium & M.intracellulare (MaMi) and M.tuberculosis

Question 18

How is leprosy treated (M. leprae) Hint: divide in 2 types

Answer 18

1. Paci-bacillary (PB) leprosy: 1-5skin lesions = 2 drugs for 6 months
2. Multi-bacillary (MB) leprosy: >5 skin lesions = 3 drugs for 12 mths