TB

Question 1

info on TB?

Answer 1

• Order: Actinomycetales
• Family: Mycobacteriaceae
• Genus: Mycobacterium
• Aerobic, non spore forming, non motile bacilli
• Slow generation time
• Lipid-rich cell wall (mycolic acids) (~40% dry
weight)
• Acid/alcohol fast bacilli (AAFB)

Question 2

classifations of myco?

Answer 2

• Obligate pathogens:
– (MTBC, M leprae)
• Skin pathogens:
– (M marinum, M ulcerans)
• Opportunistic pathogens:
– (M kansasii, M avium, M intracellulare, M xenopi)
• Non (rarely!) pathogens:
– (M gordonae, M flavescens, M smegmatis)
• Animal pathogens:
– (M paratuberculosis)

Question 3

classification: Runyon

Answer 3

• Group I: Photochromogens
– (eg M kansasii, M marinum, M simiae)

• Group II: Scotochromogens
– (eg M scrofulaceum, M szulgai, M gordonae)

• Group III: non-chromogens
– (eg M avium, M intracellulare, M xenopi, M ulcerans,
M malmoense)

• Group IV: Rapid growers
– (eg M fotuitum, M chelonae, M abscessus)

Question 4

TB drug resistance

Answer 4

• Spontaneous mutations (1x10
-7/8
)
• selection of bacilli resistant mutations
(“Acquired Resistance”)
– poor drug prescribing; poor adherence; poor supply;
poor quality
• transmission of resistant strain to new case
(“Primary Resistance”)
• Multi Drug Resistance (MDR): rifampicin &
isoniazid
• Extreme Drug Resistance (XDR): rif & inah +
injectable + fluoroquinolone

Question 5

Role of laboratory?

Answer 5

• Microscopy (auramine/ZN stain for AAFB)
• Culture (solid & liquid)
• Identification (conventional & molecular)
• Drug sensitivity testing (conventional &
molecular)
• “Serology” (gamma interferon testing)
• Molecular strain typing (MIRU-VNTR/RFLP)

Question 6

MTBC and MOTT?

Answer 6

MTBC & MAC: DNA probe (Geneprobe)

• MOTT: Genotype Mycobacterium CM kit
(HAIN Lifescience)

Question 7

sensitivity testing?

Answer 7

• Resistance ratio method
• Proportion method
• Absolute concentration (MIC broth)
• E test
• Agar disc diffusion

Question 8

drugs to test with sensitivity testing?

Answer 8

*Ethambutol
* Isoniazid
* Rifampicin
* Pyrazinamide

• Streptomycin
• Clarithromycin
• Ciprofloxacin
• Cycloserine
• Ethionamide
• Capreomycin
• Amikacin
• PAS
• Thiacetazone

Question 9

common rifampicin and isoniazid resistnce mutations?

Answer 9

rpoB, KatG & InhA

Question 10

ECAT-6 & CFP-10?

Answer 10

Encoded by RD-1 genes
• Absent from BCG
• Absent from most MOTT
• Induce IFN- responses
• Identified by immunology, genomics

Question 11

bacteria positive for bboht esat and cfp?

Answer 11

TB

M. Africanum

M. Bovis

M kansasi

M. marinum

M. Szulgai

all others are negative for both

Question 12

which method is best for detecting tb genotype?

Answer 12

Question 13

MIRU-VNTR?

Answer 13

Mycobacterial Interspersed Repetitive Units
Variable Number Tandem Repeats
• Mini satellite regions of repeating
sequences of nucleotides
• ?function, highly conserved
• Number of times the sequence repeats at
each region varies
• >40 such regions (MIRU) useful to type
strains
• 15 specific loci adopted across UK 2005
• 24 loci international standard 2010