Tuberculosis: microbiology of diagnosis and management Flashcards Preview

Yr 3 - December lectures 2018 > Tuberculosis: microbiology of diagnosis and management > Flashcards

Flashcards in Tuberculosis: microbiology of diagnosis and management Deck (22)
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What is tuberculosis?

infection caused by mycobacterium tuberculosis
- affects any part of the body
- curable following 6 months therapy

- if affecting the lungs - pulmonary
- transmission via airborne particles


What happens if you inhale TB organisms?

granuloma formation
- macrophages engulf TB (epithelioid histiocytes)
- fuse to form giant cells with central necrosis
- "ghon focus" = lung
- "ghon complex" = + lymph nodes


What is the difference between primary disease and latent infection?

primary disease = organisms continue to divide, poor immune systems

Latent infection = organism not dividing, sleeping/dormant TB


What does it mean by secondary TB?

latent TB reactivates
- organism wakes up and starts dividing
- decline in health and immunity


What are the latent TB screening methods?

Tuberculin skin test
Interferon gamma release assay (IGRA) - quantiferon and T-spot

If they react = do they have TB? if negative do they need BCG?


What is TB prevalence associated with?

poor sanitation
unpasteurized milk


What are the symptoms of TB?

Long history (slow growing organisms)
- fever => infection
- weight loss and fatigue => prolonged inflammatory state
- night sweats => TNF alpha
cough, haemoptysis, abdominal pain, headache, back pain


What are the differential diagnoses for the symptoms of TB?

fever, weight loss, night sweats
- cancer (lymphoma, leukaemia, lung, bowel, metastasis)
- infection (bacterial, fungal)

- sarcoidosis
- crohn's disease
- granulomatosis with polyangitis
- infection (fungal, parasitic)


What is the treatment for TB?

- rifampicin - 6 months
- izoniazid - 6 months
- pyrazinamide - 2 months
- ethambutol - 2 months


What is the main side effect of rifampicin?

bright orange urine


What are the treatments for drug resistant TB?

Longer = 9-24 months depending on resistance pattern
- mono/poly resistance
- multi drug resistant (MDR) = rifampicin and isoniazid
- extensively drug resistant (XDR) = MDR + quinolones and injectables


What microbiological samples need to be sent off to diagnose TB?

sputum x3
broncho-alveolar lavage
gastric lavage


What are the features of mycobacterium tuberculosis?

aerobic bacilli (upper lobes) = acid fast (neither gram +ve or -ve- has a high lipid content (mycolic acid)), slow growing
>85 species
- mycobacterium TB complex = TB, bovis (cows and human hosts), africanum = BCG
- mycobacterium lepraw
- non-tuberculos mycobacteria (NTM) - environmental, cause disease in immunocompromised pts


How are acid fast stains used to diagnose TB?

1) auramine stain (auramine phenol) => fluorescent
- "smear positive" = highly infectious
- initial screening of sputum

2) ziehl neelson stain (carbol fuchsin) => red on blue
- confirmation of mycobacteria
- can comment on morphology


How can you grow TB?

1) solid media (conventional) => lowenstein jensen (only needs one organism)

2) liquid media (rapid) => MGIT (mycobacteria growth indicator tube) = needs 1-10 organisms)


What are the new developments to increase the speed of diagnosing TB?

1) TB polymerase chain reaction (PCR)
2) whole genome sequencing (WGS)


How does TB PCR work?

(geneXpert, Xpert, Cepheid)
- straight from sputum
- detects MTBc
- can predict resistance to rifampicin
diagnose same day and 2-4 weeks to determine drug resistance


What does WGS do?

detects single nucleotide variations (polymorphisms) between 2 isolates
TB mutates at 1 SNP every 2 years
- 0-5 SNPs difference between strains = most probably linked
- 5-12 SNPs may be linked
- >12 SNPs less likely to be linked


What are the benefits of WGS?

Faster drug susceptibility prediction
- more confident treatment regimens
- less likely to induce resistance
more informed contact tracing


Where does XDR most likely originate?

likely origin is E. Europe - within transmission in the UK


Where does MDR most likely originate?

likely origin is E. Africa


What is still needed in TB diagnostics?

WGS on sputum directly
smear negative
childhood Tb - sputum hard to get
biomarkers to detect LTBI with high risk of progression to active TB