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Microbiology > Mycobacterium > Flashcards

Mycobacterium Flashcards

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Biology 101 flashcards
1
Q

General Characteristics

A
  • Thin, rod shaped
  • Obligate aerobe
  • Tough cell wall and membrane
  • Acid-Fast stain
  • Slow growing- 4-8 weeks to form colonies
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2
Q

The Unusual Structure of the Mycobacterial Cell Wall

A

Very Hearty; Very Hard to Kill

  • Lipid-rich wall is highly impermeable to regular antibiotics and dyes
  • Hardiness -> high transmissibility
  • Acid Fast Stain (3% HCl; heated): stains mycolic acid
  • Effective therapeutic targets for anti-TBs
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3
Q

Acid Fast Stain

A
  • Stains myocolic acid
  • HCl 3%, heated
  • Ziegler’s-Nielsen (ZN) Stain
    • Carbol Fuchsin binds to mycolic acid
  • Fluorochrome Stain (Sputum) - modified acid-fast; more sensative
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4
Q

Outer Membrane (mycomembrane)

A
  • High lipid content
  • Mycolic Acid - up to 90 Carbons!
  • Long chain folded and stacked
    • stacking leads to increased permeability
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5
Q

Mtb Colonies

A
  • Non-pigmented

- Lowenstein-Jensen agar: allows to observe colony and color for diagnostics

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6
Q

Mtb Gram Staining

A
  • Gram stain gives unique Ghost Stain or GP indeterminate
    • if you don’t suspect Tb but see this… suspect Tb
  • CANNOT DESTAIN MYCOBACTERIUM
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7
Q

Tuberculosis Epidemiology

A

1/3 of world infected

- S. Africa, S. Asia, Pacific Islands, N. Asian, Mongolia, N. Korea

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8
Q

Mtb Disease Overview

Pathogenesis

A
  • caught via inhalation; not everyone gets sick; long incubation
    • can also be inoculated or ingested
  • Tubercle bacilli multiply in alveolar macrophages
  • Tissue injury consequence of immune response
    • HOST DESTROYS ITSELF to control bacterial growth
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9
Q

Latent Tb

A
  • dormancy via immunity
  • no disease present because shielded by macrophages
  • most Tb infections remain latent due to delayed type hypersensitivity
    - reaction which helps diagnose via skin test
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10
Q

TB Pathology

A
  • necrosis: over growth of connective tissue

- loss of lung function leading to death

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11
Q

TST

Tuberculin Skin Testing

A
  • aka Mantoux Test
  • Antigens injected intradermally
  • look for ring of induration (not redness)2-3 days later
    • result of delayed-type hypersensitivity
      Do results depend on risk factors and patient history

> 15mm considered positive for any person

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12
Q

Problems with TST

A
  • incorrect reading
  • inconsistent interpretation
  • failure to follow up
  • cross reactivity to other mycobacterium and positive in BCG vaccinated persons
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13
Q

LTBI vs Active Disease

A

Hard to test for latent vs active because both would test positive

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14
Q

Immunodiagnosis: Interferon-y Release Assays (IGRAs)

A
  • Directly measure a person’s immune reactivity to Mtb
  • Takes time for lymphocytes to proliferate

3 Separate Measurements Obtained:

  • whole blood along: baseline
  • whole blood plus Mtb peptides: not cross reactive with BCG
  • whole blood plus non-specific activator of WBCs (nitrogen): demonstrates WBCs are present and capable of secreting IFN-y (make sure the test has potential to be correct)
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15
Q

Microbiology Test for Active TB Disease

A
  • Specimens
  • Specimen Processing
  • Direct. Detection & NAAT
  • Cultivation
  • Identification
  • Antimycobacterial Susceptibility Testing
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16
Q

TB Tests: Specimens

A
  • Sputum
  • Urine
  • Stool
  • Tissue and body fluids
  • Blood (immunocompromised persons)
  • Wounds (aspirate>swab)
17
Q

TB Tests: Direct Pathogen Visualization

A
  • Acid-fast Stain - sensitivity 20-80% (depends on patient population)
  • Fluorochrome Stain - increased sensitivity to AF

Contamination important consideration

18
Q

Cord Factor

Characteristic of Mtb

A

Cord Factor ( trehalose dimycolate)
Cording - bacteria binding to each other and aggregating
- virulence factor: toxic to phagocytes and other cells
- anti-cord antibodies are protective
- cording = probs no antibodies

19
Q

Mtb NAATs

Nucleic Acid Amplification Test

A

Use in conjunction to other testing
Turn around time similar to smear, faster than culture (remember its very slow growing)

Superior to Smear because:

  • greater specificity
  • greater sensitivity
20
Q

Mtb Cultivation

A

Always culture even if already proven to be Tb

  • Lowenstein-Jensen medium incubated for 8 weeks
    • confirms diagnosis and guides treatment
  • Liquid faster because of increased oxygen and nutrients
21
Q

MTb Identification

A
  • Acid Fast Stain
  • Nucleic Acid Probes
  • Probe negative isolates require additional work
    • morphology

Microbiology (7 decks)

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