TB Genomics

Question 1

what is TB?

Answer 1

a contagious, debilitating (consuming) bacterial disease

spread by airborne droplets from an infected person

Question 2

what is TB caused by?

Answer 2

Caused by a bacterium
•
Mycobacterium tuberculosis
•   slow growing, difficult to kill, waxy coat
•   coughing
speaking
sneezing
•   Left untreated, one person with tuberculosis
will infect 10-15 people

Question 3

what are the sites of infection in TB?

Answer 3

85% pulmonary TB

15% extra-pulmonary TB

HIV - only 30% pulmonary

Question 4

spread of infection via hematogenous spread includes:

Answer 4

Pleural disease
Lymph nodes – scrofula
Pericardial
Skeletal –Potts disease
Genitourinary
Gut
Peritoneal
Miliary
Meningeal

Question 5

what are the risk factors for TB?

Answer 5

Old Age – very young
• HIV
• Drugs
• Diabetes
• Chronic renal disease
• Malnutrition  - vitamin D?
• Malignancy (lymphoma, leukaemia)
• Lung disease
co-morbidities and exposure
poverty
immunocompromised states

Question 6

TB stats

Answer 6

in 2011 12mill w TB worldwide
1/3 world latenty infected
9000 cases in UK

Question 7

how to treat TB?

Answer 7

antibiotics 1943 - streptomycin

post 1973 4 drug combo trials:
isoniazid
rifampicin
pyrazinamide
ethambutol

Question 8

why must treatment contain multiple drugs to which organisms are suceptible?

Answer 8

Treatment with a single drug or adding a single drug
to failing regimen can lead to the development of
drug-resistant TB

High bacterial load in TB (unique)

Selection of
pre-existing
resistant mutants

Question 9

what does izoniazid do?

Answer 9

inhibits the synthesis of mycolic acids, which are required components of the mycobacterial cell wall.

Question 10

what does ethambutol do?

Answer 10

disrupts arabinogalactan synthesis by inhibiting the enzyme arabinosyl. Disruption of the arabinogalactan synthesis inhibits the formation mycolyl-arabinogalactan-peptidoglycan complex in the cell wall.

Question 11

what does rifampicin do?

Answer 11

inhibits bacterial RNA polymerase

Question 12

what does pyrazinamide do?

Answer 12

binds to the ribosomal protein S1 (RpsA)

and inhibits translation + other possible mechanisms

Question 13

which drugs are prodrugs?

Answer 13

pyrazinamidase and isoniazid

Question 14

how is pryazinamidase converted to active acid form?

Answer 14

by PncA - pryazinamidase (PZase) enzyme

Question 15

what is the personalised response to treatment?

Answer 15

• Response to treatment is highly variable
due to many host factors
- disease type and extent, immuno-competence,

Measure Sputum Culture Conversion at 2 months
- good indicator of effective treatment.

Bacterial strain - genotype-phenotype
- antibiotic resistance

Question 16

factord that increase chance of drug resistance in TB

Answer 16

Patient has spent time with someone with active drug-resistant TB disease

Patient does not take their medicine
regularly

Patient does not take
all
of their medicine

Patient develops active TB disease after having taken TB medicine in the
past

Patient comes from area of the world where drug-resistant TB is common

Question 17

how to mutations occur?

Answer 17

spontaneously develop as bacilli proliferate

Question 18

what is extensive drug resistance? (XDR)

Answer 18

XDR-TB is MDR-TB that is resistant to any fluoroquinolone and at least one of three
injectable second-line drugs (capreomycin, kanamycin, and amikacin)

Question 19

how do we detect drug resistance in TB

Answer 19

Standard methods

- culture and phenotypic drug susceptibility testing (DST) t

Question 20

how long does DST take and whats the problem with this?

Answer 20

weeks to months
delays during which patients recieve sub-optimal therapy this leads to additional resistance and further spread of durg resistant TB

Question 21

biological potential in TB?

Answer 21

slow growth, dormancy, intracellular pathogen, complex cell wall

Question 22

what are the drug resistance mechanisms?

Answer 22

1)Barrier mechanisms (decreased permeability and efflux pump)

2) degrading or
inactivating enzymes
(e.g. β-lactamases)

3) modification of pathways involved in drug activation
or drug metabolism (e.g.
katG and isoniazid resistance)

4) drug target modification (e.g. rpoB and rifampicin
resistance)

5) target amplification (e.g.
inhA and isoniazid resistance)

Question 23

how does genome seq inform complex treatment for drug resistant TB?

Answer 23

1) tb patient xray
2) genome of m.tuberculosis
3) dna seq and bioinformatic analysis
4) defines mutation
5) infoms complex 2 year drug treatment regimen for XDR TB

Question 24

what do genotypic tests depend on?

Answer 24

strength of associations

Question 25

MDR-TB Clinical case 1

Answer 25

MDR-TB clinical case 1
A 26 year old Georgian man –drug resistant tuberculosis.
Treated for tuberculosis 18 months earlier, standard short-course quadruple therapy for 6 months.
Following completion of this course of therapy he was informed he had not been cured
Antimicrobial drugs required for MDRTB unavailable in Georgia.
The patient also reported that he had been imprisoned whilst in Georgia.

Question 26

what is the inclusion and dosage of Isoniazid dependant on?

Answer 26

it is dependant on the genotype detected

katG mutation detected - associated with high level resistance (isoniazid therapy not incl)

inhA mutation detected - genotype associated with low level resistance (isoniazid therapy incl but no ethionamide)