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Clinical food and microbiology > 5. Tuberculosis > Flashcards

5. Tuberculosis Flashcards

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1
Q

What is Tuberculosis?

A
  • 1.4 millions deaths in developing nations
  • Respiratory TB/ Non-respiratory TB
  • caused by Mycobacterium Tuberculosis; M.africanum, M. bovis, M.microti, M.absessus, M.canetii
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2
Q

How can you get TB?

A
  • close contacts of infected cases
  • travelling to endemic regions
  • immuno-compromised immune system; HIV
  • elderly
  • homeless, drug abusers, alcoholics
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3
Q

What mycobacteria species are in humans and what does it cause?

A

M. tuberculosis
M. africanum
M. microti
M. canetii
- Tuberculosis

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4
Q

What mycobacterium resides in animals?

A

M. bovis
- Bovine TB

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5
Q

What bacterium resides insides in humans ad armadillos?

A

M. leprae
- Leprosy

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6
Q

What mycobacterium resides in environment and water systems?

A

M. absessus
- only affects those with fibrosis/ bronchiectasis

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7
Q

What mycobacterium is present in birds?

A

M. avium-intracellulare
- TB-like lung infection/ disseminated in AIDS patients

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8
Q

What are characteristics for the Mycobacterium species?

A
  • Phylum: Actinobacteria; filamentous
  • Acid fast: cell envelope contains 60% long chain branched hydrocarbons
  • has a virulence factor: mycolic acid
  • has a cord factor: Trehalose dimycolate (TDM)
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9
Q

What are the roles of Mycobacterium?

A
  • reduce permeability to other molecules; confers resistance to chemicals, stains, antibiotics
  • confers resistance to drying
  • intracellular survival
  • slow growing: generation time 15-22 hours (cf 1 hour staphylococci)
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10
Q

What is stage 1 of tuberculosis pathogenesis?

A

Inhalation of infectious particles: droplet nuclei (5micrometers, approx 3 bai=cilli)

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11
Q

What is stage 2 of tuberculosis pathogenicity?

A
  • after 7-21 days. MTB multiplies with macrophages intracellularly
  • Macrophages secrete IL-2 and present MTB antigen on their surface
  • they eventually burst liberating MTB
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12
Q

What is the third stage of tuberculosis pathogenicity?

A
  • IL-2 stimulates T-lymphocytes (CD4+8) to infiltrate, recognise MTB antigen and become sensitised
  • CD4 release inflammatory cytokines, IFN-gamma resulting in tubercle formation (primary lesion)
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13
Q

What is the fourth stage of M. tuberculosis pathogenesis?

A
  • MTB continues to multiply within inactivated/ poorly activated macrophages and tubercle expands
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14
Q

What is the fifth stage of M. tuberculosis pathogenesis?

A

The primary lesion heals: forming GHON focus- type of granuloma

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15
Q

How does latency to infection occur?

A

Bacteria ceases to grow and lesion calcifies (90%) and this causes reactivation

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16
Q

What happens in active TB infection?

A
  • the lesion liquifies and bacteria spreads to lungs/organs
  • bacteria coughed up in sputum
17
Q

What is primary tuberculosis?

A

can be:
-immunocompetent host:
CMI prevents spread of M. tuberculosis, so no symptoms.
latent TB, reactivation may occur

-immunocompromised host:
primary focus worsens; pneumonia develops to LRTI. systemic dissemination.
symptoms result from CMI response: chronic inflammation (has no endotoxin/exotoxin).

18
Q

What is secondary TB?

A

endogenous- reactivation of initial infection (within 2 years)
- associated with impairments in CMI and local disturbance of dormant tubercles
- caseous necrotic lesions develop which liquify and leave discharge into bronchi

19
Q

How does mycobacteria affects AIDS patients?

A
  • 2/3 AIDS patients in sub-saharan Africa develop TB
  • prone to rapid primary infection and reactivation of previous infection
  • prone to disseminated MAC (M.avium complex) infection
  • AIDS patients are very susceptible to M.avium intracellulare
20
Q

What are the symptoms of tuberculosis?

A
  • 90% of TB patients asymptomatic
  • 10% leads to primary TB
  • LRTI; cough, fever, weight loss, faitgue
  • Military TB: meningitis, septicaemia, kidney infection, joint infection (Pott disease)
21
Q

What is the clinical diagnosis of TB?

A
  • presenting symptoms
  • radiological changes on chest xray
  • Tuberculin skin test (TST); Mantoux test, injection with purified protein derivative (PPD)
22
Q

What is the laboratory diagnosis of TB?

A

Non-culture techniques:
- IGRA: interferon gamma release assay
- molecular detection in clinical samples, eg..Nucleic acid amplification, PCR
- Microscopy

Culture techniques:
- culture; gold standard method MGIT

23
Q

What is the diagnostic microbiology of TB?

A
  • early morning sputum x3
  • renal TB; complete EMU x3
  • CSF; meningitis
  • lymph node biopsy
  • blood/ bone marrow aspirate
  • whole blood; IGRA
24
Q

How would you use IGRA for TB diagnosis?

A
  • patient sample with possible active or latent TB is re-exposed to specific mycobacterial antigens
  • antigens utilised are encoded in region of difference (RD)1
  • RD1 encoded antigens are; early secretary antigenic target ESAT-6 and culture filtrate protein CFP-10

can use commercial kits

25
Q

What staining is used for mycobacterium microscopy?

A

Ziehl-Neelson stain
- lower limit of detection of ZN stain 5x103 orgs/mL
- 100x objective lens

Fluorescent Auramine stain
- 40x objective lens
- positive results within hour
- negative result does not rule out TB

26
Q

What is (gold standard) culture for respiratory TB?

A

sample prep:
- liquefaction of sputum
- concentration
- decontamination

culture:
- solid culture; Lowenstein Jensen slopes, incubation at 37 for 8 weeks
- broth culture; BACTEC mycobacterial broth

27
Q

How can you fully identify M. tuberculosis colonies?

A
  • colonial appearance
  • ZN positive colonies
  • Biochemical characteristics
  • Rapid ID molecular probes
28
Q

What are the current guidelines for treatment of respiratory TB?

A

BTS- British Thoracic Society
NICE - National institute for Health and Care Excellence

29
Q

What is MDR-TB?

A

It is multi-drug resistant TB.
It has resistance to at least isoniazid and rifampicin.

30
Q

What medication is administrated for active TB?

A

initial phase: rifater
- isoniazid, rifampicin, pyrazinamide, ethambutol

continuation phase: rifinah 300 or rimactazid 300
isoniazid, rifampicin

Clinical food and microbiology (12 decks)

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