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Microbiology test 2 > Lect 14 > Flashcards

Lect 14 Flashcards

1
Q

Mycobacterium tuberculosis: reservoir and transmission

A
  • humans are only reservoir
  • transmission: aerosol
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2
Q

MTB Strains vary in antibiotic susceptiblity. name the strains

A

MDR strains - multi-drug resistant XDR strains - extensively drug resistant

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3
Q

MTB Bimodal Age Distribution of disease. Name the ages and also what type of dissemination occurs in these patients

A
  • Infants and Older Adults
    • Infants and Immunocompromised - Hematogenous dissemination Can result in meningitis and other symptoms
    • Older - Failure of immune system - Possible reactivation of latent infection
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4
Q

MTB initial infection risk factors

A
  • close contact with TB case: • Many children become infected by caregivers
  • Residence in long-term care facility
  • Low income/inner city housing
  • Alcoholism or IV Drug Use
  • Diabetes mellitus (30% increase over lifetime)
  • Silicosis - pneumoconiosis- inhalation silica dust
  • Immunosuppression
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5
Q

Name the three species that produces human tuberculosis

A
  1. mycobacterium tuberculosis
  2. mycobacterium bovis
  3. mycobacterium aficanum
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6
Q

which mycobacterium is the source of the BCG vaccine

A

mycobacterium bovis

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7
Q

MTB

  • shape
  • motility
  • oxygen?
A
  • bacillus
  • non motile
  • obligate aerobes
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8
Q

MTB is killed by what process that we do to milk

A
  • pasteurization
  • *heat sensitive
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9
Q

where does MTB grow

A
  • intracellular growth - alveolar macrophages
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10
Q

MTB undergo what type of staining

A
  • MTB cells resist normal gram stain: acid fast bacilli
  • harsh treatment is used: ziehl-neelsen or Kinyoun stains
  • MTB cells, once stained, will not decolorize
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11
Q

describe cell wall of mycobacterium tuberculosis

A
  • outer layer: mycolic acid
  • inner layer: peptidoglycan
  • **cell wall Influences staining behavior, produces slow growth phenotype and confounds antibiotic therapy
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12
Q

MTB virulence factors

A
  • No classic virulence factors or toxins
  • structure enables it to persist as an intracellular pathogen
    • mycolic acid: prevent dehydration and may resist H2O2
    • cord factor
      • Mycoside – glycolipid Mycolic acid + disaccharide
    • lipoarabinomannan: Inhibits cell-mediated immunity
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13
Q

MTB infection potential outcomes

A
  1. immediate resolution
  2. primary disease
  3. progressive primary (active disease)
  4. latent infection
  5. endogenous reactivation/secondary disease
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14
Q

how does MTB cause cell and tissue destruction

A
  • After phagocytosis by macrophages, MTB specifically prevents fusion with lysosomes while allowing nutrient-containing vesicles to merge.
  • Innate and cell-mediated host immune responses to MTB produces selfdestruction of cells and tissues
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15
Q

what structure becomes evident 2-6 weeks after MTB infection

A
  • granulomas: areas surrounded by macrophages, fibroblasts, and collagen fibers harboring viable MTB cells
    • over time, can form fibrotic tubercle and calcify-> tubercles or Ghon bodies.
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16
Q

Does person infected with latent TB able to spread disease

A
  • bacteria remain viable in lesions but inactive
  • patients have no symptoms
  • no risk to spread disease
17
Q

what happens to a patient when latent TB becomes reactivated-> secondary TB

A
  • Granulomas: Erode and discharge TB bacilli into bronchi (infectious)
    • Erode blood vessel – hematogenous spread to other body sites – TB can involve any organ
  • signs and symptoms are present; patient is infectious
  • cough, weight loss, fatigue, fever, night sweats, chest pain
18
Q

what is miliary tuberculosis

A
  • results from lymphohematogenous spread of primary infection or via a latent focus with subsequent spread
  • **massive spread of agent
19
Q

What means are available to help aid diagnosis of TB

A
  • skin test
  • xray consistent with TB
  • sputum stain/broth culture to detect acid fast bacteria
20
Q

describe Serial screening programs

A
  • Use purified MTB protein derivative (PPD) in tuberculin skin test (Mantoux skin test)
  • Small amount of antigen injected under the skin, size of induration measured after 48-72 hours
  • Boosters (persons with earlier infection with minimal reaction to PPD) are identified by quick second administration
21
Q

what can cause a false positive on TB skin test

A

BCG recipients and those infected with NTM may react as false positives

22
Q

length of treatment for active TB disease

A

extended duration (6-9 months), multi-drug regimen requiring patient compliance

23
Q

treament for latent TB

A

Isoniazid (9 months)

24
Q

Mycobacterium avium complex (MAC)

  • gram status
  • oxygen?
  • where is it found
A
  • gram positive
  • aerobic
  • ubiquitous
    • water, soil, plants
25
Q

Mycobacterium avium complex (MAC) require what staining

A

acid fast

26
Q

transmission of Mycobacterium avium complex (MAC)

A
  • ingestion of contaminated water or food
  • **NO person to person transmission
  • **NO patient isolation required
27
Q

Mycobacterium avium complex (MAC) are known to infect what patient populations

A
  • opportunistic human pathogens
  • HIV
28
Q

Mycobacterium avium complex (MAC) causes what in middle aged and older males with history of smoking

A

Cavitary lesions resemble TB

29
Q

Mycobacterium avium complex (MAC) causes what in elderly female non-smokers

A
  • Patchy or nodular on X-ray
  • Lady Windermere’s syndrome
30
Q

MAC causes what in AIDS patients

A

Disseminated disease, no organ spared as immune system collapses

31
Q

how is Non-tuberculous Mycobacterial Infections (NTM) – the Mycobacterium avium Complex (MAC) diagnosed

A
  • clinical illness
  • microscopy to reveal acid-fast bacteria and culture
32
Q

general rules for MAC treatment

A
  • Both HIV positive and HIV negative patients use combination therapy
  • Take HIV infection status into account
33
Q

MAC treatment length in HIV negative patients

A

Continue until sputum cultures are negative for 1 year

34
Q

HIV positive patients take what prophylactically to prevent MAC infection

A
  • Chemoprophylaxis with CD4 100 cell/µL
  • Can discontinue 3 months after CD4 >100 cell/µL
35
Q

Treatment In HIV+ patient with MAC infection

A
  • Without immune reconstitution – lifelong
  • Or begin treatment for 2 weeks then anti-retroviral (HAART) therapy

Microbiology test 2 (6 decks)

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