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Bacteriology > Mycobacteria > Flashcards

Mycobacteria Flashcards

1
Q

What is unique about the cell wall of mycobacteria?

A

Contain mycolic acids, very lipid rich

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2
Q

What staining procedure is used for mycobacteria?

A

Acid fast

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3
Q

What are the antigens in a Tuberculin Skin Test directed towards?

A

PPD polypeptides in the cell wall

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4
Q

Which mycobacteria is extremely slow growing?

A

M. Leprae

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5
Q

From which mycobacteria strain is BCG (the TB vaccine) derived from?

A

M. bovis

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6
Q

On what medium do you grow M. tuberculosis?

A

Lowenstein-Jensen (L-J) medium

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7
Q

How does M. tuberculosis appear in liquid medium?

A

Cording (cord factor)

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8
Q

How can M. tuberculosis and M. bovis be differentiated with biochemical tests?

A

Both are nitrate reductase positive
M. tuberculosis is niacin positive
M. bovis is niacin negative

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9
Q

What cells primarily mediate the immune response to M. tuberculosis?

A

CD4+ T cells (specifically Th1) that secrete IFNgamma and macrophages

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10
Q

How is the mycobacteria tuberculosis contained?

A

Granuloma formation by the T cells and macrophages

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11
Q

What cytokine is necessary for macrophage response and granuloma formation to contain M. tuberculosis?

A

TNFalpha (remember not to give TNFalpha inhibitors to people at risk of recurrent TB infection)

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12
Q

Which test for tuberculosis can differentiate between BCG vaccine and active M. tuberculosis?

A

IGRA (QuantiFERON-TB Gold test (blood test))

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13
Q

How does drug resistance develop in Mycobacterium?

A

Point mutations

NOT plasmid or transposons

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14
Q

How can we grow Mycobacterium leprae?

A

Armadillos and mice

Cannot culture

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15
Q

Tuberculoid v. Lepromatous M. leprae

A

Tuberculoid - Th1 predominance, few skin lesions, single nerve involvement
Lepromatous - Th2 predominance, many lesions, several nerves affected

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16
Q

What is the hallmark clinical feature of M. leprae?

A

Anesthetic skin lesion + thickened peripheral nerve

17
Q

How is TB most commonly transmitted?

A

Inhalation of infectious droplets from another person with smear positive pulmonary TB

18
Q

What is the primary lesion in lung of TB patient called?

A

Ghon focus

19
Q

What are the outcomes of primary TB?

A
  • Usually Ghon focus heals with calcification, TB is latent

- Some bacilli can spread in blood stream and cause primary TB disease

20
Q

What are some defining characteristics of a latent TB infection?

A
  • Positive PPD
  • Absence of any clinical symptoms
  • Normal CXR (or could have calcification of Ghon focus)
  • Negative smear or culture
21
Q

What are the steps in diagnosis/management of latent TB infection?

A
  • Screen patients at increased risk
  • Perform and interpret screening tests (TST or IGRA)
  • If test is positive, rule out active TB with phys exam and CXR
  • Assess risks and benefits of LTBI treatment and treat if necessary
22
Q

What is the preferred treatment for latent TB?

A

Isoniazid daily x 9 months

23
Q

What is the hallmark of reactivated TB on a CXR?

A

Cavitation in upper lobes

24
Q

What are diseases that manifest from extrapulmonary tuberculosis?

A
  • Basilar meningitis
  • Pott’s disease (Gibbus formation of vertebral collapse)
  • Miliary tuberculosis (Millet seed lesions on CXR)
  • Lymphadenitis
25
Q

What is different about treatment of latent TB v. active TB?

A

Active TB requires multi drug combination therapy, latent can be treated with just Isoniazid.

26
Q

What are the different phases of active TB drug therapy and what do they consist of?

A

Intensive phase: 2 months, 4 drugs (2x4)

Continuation phase: 4 months, 2 drugs (4x2)

27
Q

What must be given with Isoniazid to prevent nerve damage?

A

Vitamin B6

28
Q

What is the method of transmission of Non-tuberculosis mycobacteria?

A

Inhalation, ingestion, or inoculum, but NO person to person

Bacteriology (19 decks)

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