TB Genomics Flashcards
what is TB?
a contagious, debilitating (consuming) bacterial disease
spread by airborne droplets from an infected person
what is TB caused by?
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
what are the sites of infection in TB?
85% pulmonary TB
15% extra-pulmonary TB
HIV - only 30% pulmonary
spread of infection via hematogenous spread includes:
Pleural disease Lymph nodes – scrofula Pericardial Skeletal –Potts disease Genitourinary Gut Peritoneal Miliary Meningeal
what are the risk factors for TB?
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
TB stats
in 2011 12mill w TB worldwide
1/3 world latenty infected
9000 cases in UK
how to treat TB?
antibiotics 1943 - streptomycin
post 1973 4 drug combo trials: isoniazid rifampicin pyrazinamide ethambutol
why must treatment contain multiple drugs to which organisms are suceptible?
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
what does izoniazid do?
inhibits the synthesis of mycolic acids, which are required components of the mycobacterial cell wall.
what does ethambutol do?
disrupts arabinogalactan synthesis by inhibiting the enzyme arabinosyl. Disruption of the arabinogalactan synthesis inhibits the formation mycolyl-arabinogalactan-peptidoglycan complex in the cell wall.
what does rifampicin do?
inhibits bacterial RNA polymerase
what does pyrazinamide do?
binds to the ribosomal protein S1 (RpsA)
and inhibits translation + other possible mechanisms
which drugs are prodrugs?
pyrazinamidase and isoniazid
how is pryazinamidase converted to active acid form?
by PncA - pryazinamidase (PZase) enzyme
what is the personalised response to treatment?
• 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
factord that increase chance of drug resistance in TB
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
how to mutations occur?
spontaneously develop as bacilli proliferate
what is extensive drug resistance? (XDR)
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)
how do we detect drug resistance in TB
Standard methods
- culture and phenotypic drug susceptibility testing (DST) t
how long does DST take and whats the problem with this?
weeks to months
delays during which patients recieve sub-optimal therapy this leads to additional resistance and further spread of durg resistant TB
biological potential in TB?
slow growth, dormancy, intracellular pathogen, complex cell wall
what are the drug resistance mechanisms?
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)
how does genome seq inform complex treatment for drug resistant TB?
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
what do genotypic tests depend on?
strength of associations
MDR-TB Clinical case 1
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.
what is the inclusion and dosage of Isoniazid dependant on?
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)
