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Bacteria > Mycobacterium > Flashcards

Mycobacterium Flashcards

1
Q

Common characteristics (5)

A

Aerobic bacillus

Replicate slowly

Intracellular pathogens

Resist ordinary stains

Acid-Fast Bacilli

(non-motile, non-sporing)

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2
Q

Why do mycobacterium resist ordinary stains?

A

HIGH proportion of LIPID (MYCOLIC ACID) and GLYCOLIPID in CELL WALL

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3
Q

What has the high concentration of lipid in their cell wall been associated with? (5)

A

1- Impermeability to stains and dyes

2- Resistance to many antibiotics

3- Resistance to killing by acidic/alkaline compounds

4- Resistance to osmotic lysis via complement deposition

5- Resistance to lethal oxidations and survival inside macrophages —> Intracellular pathogens

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4
Q

Stains (2)

A

Ziehl-Neelsen Stain (Confirmatory if Auramine +ve) —> Magenta
1- Carbon fuschin
2- Decolorize with Acid alcohol
3- Counterstain with Methylene blue

Auramine stain (Flourochrome stain) —> Yellow

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5
Q

Ghon Focus

A

Inhalation of infectious droplet nuclei —> Alveoli (englufed by macrophages) —> Multiply and produce cytokines e.g. TNF-a —> Inflammation and Caseous Necrosis

(Alveoli)

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6
Q

Ghon Complex

A

Bacilli spread to regional lymph node —> AFB proliferate —> Ghon complex —>Lung lesion and Hilar Lymph node

(Alveoli and Lymph Node)

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7
Q

Infection can either be.. (2)

A

1- Quiscent (dormant)

2- Progress lung disease or disseminate (Miliary TB)

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8
Q

Reactivation (2)

A

Later in life, especially if immuno-compromised

NO SYMPTOMS but detected using PPD or IGRA

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9
Q

What does Miliary TB cause?

A

Lesions resembling Millet seeds

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10
Q

Virulence Factor: Intracellular Growth

A

Phagocytosis INHIBIT PHAGOSOME-LYSOSOME FUSION by secretion of protein e.g. Heat-shock proteins that modify phagosome membrane

Live in protected environment for growth

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11
Q

Virulence Factor: Detoxification of Oxygen Radicals

A

MTB interferes with toxic effects of reactive oxygen intermediates produced in process of phagocytosis

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12
Q

Virulence Factor: Antigen 85 Complex

A

Group of proteins secreted by MTB known to BIND FIBRONECTIN

Aid in WALLING OFF bacteria from immune system and may facilitate TUBERCLE formation (skin irritation)

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13
Q

Virulence Factor: Slow Generation Time

A

Immune system may not recognize bacteria or may not be triggered sufficiently to eliminate them

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14
Q

Virulence Factor: High Lipid Concentration in Cell Wall

A

Impermeability and resistance to anti microbial agents

Resistance to killing by acidic and alkaline compounds in both Intracellular and extracellular environment

Resistance to osmotic lysis via complement deposition and attack by lysozyme

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15
Q

Infections by MTB

A

Pulmonary TB: Pneumonia, Pleural Effusion

Extra-Pulmonary TB: Lymph node enlargement, Meningitis, Renal TB, Bone+Joints

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16
Q

Culture (2)

A

Solid Media: Lowenstein-Jensen Media (GREEN)

Liquid Media: MGIT (Mycobacterial Growth Indicator Tube)

17
Q

Diagnosis (3)

A

1- Tuberculin Skin Test

2- PPD (Purified Protein Derivative) (Intradermal Injection)

3- IGRA (Interferon Gamma-Release Assay)

18
Q

PPD

A

Read after 2-3 days, Induration

> 10mm = Positive and <5mm = Negative

False Negative —> HIV

False Positive —> NTM

19
Q

IGRA

A

Measure interferon-gamma released from T cells after stimulation with specific M.tuberculosis antigen e.g.

  • T Spot Test
  • Quanti-FERON-TB Test

(+): Not affected by previous BCG or NTM
Needs one patient visit

(-): Does not replace smear microscopy or culture
Does not distinguish active and latent

20
Q

Rapidly growing MOTT (3)

A

M.cholenei

M.abscessus

M.fortuitum

21
Q

Slowly growing MOTT (2)

A

M.avium-intracellulare complex (MAC)

M.kansasi

22
Q

Intermediately growing MMOT

A

M.marinum

23
Q

MOTT: Chronic Lung Disease (2)

A

MAC

M.kansasi

24
Q

MOTT: Cervical Lymphadenitis (1)

A

MAC

25
Q

MOTT: Skin and Soft Tissue Infection (4)

A

M.chelonei

M.marinum

M.fortuitum

M.abscessus

26
Q

MOTT: Disseminated Infection (1)

A

MAC

27
Q

MOTT: Catheter Related Infection (2)

A

M.abscessus

M.fortuitum

28
Q

Scotochromagen (Both light and dark)

A

M.scrofulaceum

29
Q

Non-chromagen

A

MAC

30
Q

Photochromagen (Produce pigment only in presence of light)

A

M.kansasi

31
Q

Mycobacterium Leprae (2)

A

Leprosy

Human = ONLY HOST

32
Q

M.leprae (2)

A

Close contact

Nasal droplet

33
Q

M.leprae Pathogenesis (3)

A

LIPID CAPSULE (PHENOLIC GLYCOLIPID 1) —> INTRACELLULAR survival —> LOW ANTIBIOTIC penetration

34
Q

M.leprae Clinical Manifestations (3)

A

Skin lesions
Peripheral Neuropathy
Deformity ulcer e.g. loss of digits

35
Q

Lepromatous Leprosy

A

Diffuse Lesions

High organisms

36
Q

Tuberculoid Leprosy

A

Localized Lesion

Low organisms

37
Q

M.leprae Diagnosis

A

Experiment infection of mouse footpad

Bacteria (24 decks)

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