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micro_db > Micro 10-Mycobacteria > Flashcards

Micro 10-Mycobacteria Flashcards

1
Q

what is the Mycobacterium Tuberculosis complex?

A

a genetically related group of Mycobacterium species that can cause tuberculosis in humans or other animals and include M tuberculosis, M bovis, M. africanum

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2
Q

name few important non-tuberculosis mycobacteria

A

M. kansasii, M. xenopi, MAI— M. avium-intracellulare complex, M. chelonae, M. leprae

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3
Q

Mycobacteria are aerobic or anaerobic?

A

aerobic

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4
Q

Mycobacteria genus includes only pathogens.True/False.

A

False.

The genus includes obligate & opportunistic pathogens; saprophytes

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5
Q

what is the most important characteristic of the cell wall of mycobacteria?

A

•The cell wall has a high lipid content

  • Difficult to stain with commonly used dyes in laboratory
  • Resist decolorization by acid & acid-fast bacilli
  • Resistant to common antibacterial agents
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6
Q

Mycobacteria can be grown on blood agar. True/False

A

False

• Do not grow on conventional agar plates such as blood; need special media

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7
Q

slow vs fast-growing mycobacteria?

A
  • Slow growers take 3-6 weeks to grow; dividing time is 12-24h, e.g. M. tuberculosis, require 3-8 weeks incubation
  • Fast-growing mycobacteria (e.g. M. chelonae, M. abscessus) positive within 1-2 weeks
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8
Q

what are the major contributory factors for MTB infection?

A

•Poverty, overcrowding, malnutrition/famine, major contributory factors

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9
Q

Patients with latent TB can transmit the infection. True/False.

A

False.
•Transmission occurs from the person with infectious, not latent TB infection
•Expelled when the person with infectious TB coughs, sneezes, speaks (respiratory TB)
•Close contacts at highest risk of becoming infected

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10
Q

what medical conditions increase the risk of MTB infection to progress to TB?

A
  • HIV (10% progress in one year versus 10% lifetime risk in non-HIV)
  • Prolonged corticosteroid therapy
  • Other immunosuppressive therapy
  • Recent infection with TB
  • Diabetes mellitus
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11
Q

what is the presentation of primary TB?

A

Primary TB may mimic community-acquired pneumonia but with persistent symptoms

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12
Q

miliary TB involves what organs?

A

Miliary spread may involve the liver, spleen, lymph nodes, adrenal, bones & fallopian tubes (tubercles= granulomas)
May get pleural effusions

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13
Q

what is secondary TB?

A

Secondary/post-primary/’adult’ TB occurs in a previously sensitized person

a) Can be reactivation of dormant infection – common in Ireland
a) Exogenous re-infection

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14
Q

describe the features of secondary TB

A

1) cavitation +/-hemoptysis
2) localized to the lung
3) bloodstream invasion is unusual
4) no lymph node involvement

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15
Q

name common extra-pulmonary sites of TB?

A
  • Pleura
  • Central nervous system
  • Lymphatic system
  • Genitourinary
  • GIT (M. bovis ingested in contaminated milk)
  • Bones & joints
  • Disseminated (miliary TB)
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16
Q

what type of Mycobacteria commonly involve the Gastrointestinal tract?

A

M. bovis, commonly ingested by cow milk

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17
Q

name a few systemic symptoms concerning TB?

A

weight loss, night sweats over weeks & not days, fever, malaise, anorexia

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18
Q

TB is a common cause of Fever of unknown origin (T/F)

A

True

a common cause of FUO in endemic areas nonresponsive to antibiotics.

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19
Q

what tests are used to diagnose latent TB and previous exposure to TB?

A

Skin tests. i.e

  • Mantoux, Heaf
  • Interferon-gamma release assay (IGRA)

also used for screening

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20
Q

what test is described by intradermal injection of protein derivative of tuberculin?

A

PPD/Mantoux

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21
Q

what type of hypersensitivity reaction is the basis of the PPD test?

A

delayed-type cell-mediated hypersensitivity (type 4, T cell-mediated)– usually develops 3-9 wks after infection

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22
Q

negative PPD test excludes TB. True/False.

A

False
.+ ve recent or previous TB, previously vaccinated.
Can be negative at very early infection, disseminated disease or immunosuppressed

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23
Q

PPD test is affected by BCG vaccination. True/False.

A 
True
vs IGRA (not affected by vaccination, advantage)
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24
Q

PPD testing is useful in persons with active infection.

True/False.

A

False.
Tuberculin skin testing useful for a person who is not ill but may be infected. Useful to determine how many people in a group are infected

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25
Q

what is the trade name for IGRA (interferon-gamma releasing assay)

A

QuantiFERRON

26
Q

what is the advantage of IGRA against PPD?

A

Not affected by BCG vaccine but does not distinguish active from latent TB

27
Q

describe the mechanism of IGRA.

A

Whole blood assay that detects the release of interferon-gamma by sensitized cells incubated with M. tuberculosis peptides or proteins

28
Q

what body specimens are used to microscopically identify MTB?

A

sputum, early morning urine (EMU), CSF, pus, tissue

29
Q

what stains are used to identify MTB?

1) Ziehl–Neelsen stain
2) auramine-rhodamine stain
3) silver stain
4) PAS stain

A

Zhiel Nielsen and auramine rhodamine (uses fluorescence microscopy).

30
Q

what agar is used to grow MTB?

A

Lowenstein Jensen (LJ)- Automated liquid culture with radiometric detection of 14CO2

31
Q

what is the role of PCR in MTB diagnosis?

A

to confirm identity/resistance genes, diagnosis of microscopy - ve but still suspected cases

32
Q

what is the TB suggestive finding on chest X-ray?

A

apical cavitation

33
Q

what is the most famous feature of TB on tissue histology specimens?

A

caseating granulomata in tissues (a type of necrosis, the outlines of cells are not preserved at the center of necrosis)

34
Q

name the principles of TB treatment?

A
  • Combination therapy
  • Months and not days of antibiotics
  • Different agents to conventional antibiotics
  • Drugs that penetrate intra-cellularly
  • Regimen governed by susceptibility results
  • Treatment at least 6/12 depending on site of infection
  • Pulmonary TB - Initial start on 4 drugs 2/12 & then rationalized, based on results to 2 agents x 4/12
35
Q

how many drugs initially are used to treat TB?

A

4

36
Q

First-line drugs for the treatment of TB are:

  • Isoniazid (INH)
  • streptomycin
  • ethambutol
  • pyrazinamide

True/False

A

False.

Instead of streptomycin, rifampin is used

37
Q

name second-line agents of TB

A 
streptomycin
kanamycin
moxifloxacin
amikacin
ethionamide
capreomycin
P-aminosalicylic acid
38
Q

do drugs used to treat TB need to work intracellularly or extracellularly?

A

Intra as MTB is an intracellular organism

39
Q

rifampicin can cause peripheral neuropathy as a side effect. True/False

A

False.

It can cause hepatitis, peripheral neuropathy can be caused by INH which affect vitamin B6 absorption

40
Q

what is the famous side effect of ethambutol?

A

optic neuritis

41
Q

what are the side effects of pyrazinamide?

A

precipitate gout

hepatotoxicity

42
Q

INH x 6 month or INH+ rifampin x 3 months are used for the treatment of what kind of TB?

A

latent TB

43
Q

describe primary vs secondary drug resistance of MTB?

A
  • Primary resistance: a patient initially infected with resistant organisms
  • Secondary resistance (acquired resistance) develops during TB therapy
44
Q

what are the risk factors of drug resistance?

A
  • History of treatment with TB drugs
  • Contacts of drug-resistant TB
  • Foreign-born persons from high prevalent drug-resistant areas
  • Smears or cultures remain positive despite 2 months of TB treatment
  • Received inadequate treatment regimens for >2 weeks
45
Q

MTB resistant to INHand rifampin +/- other drug is called?

A

Multi-Drug Resistant TB (MDRTB)

46
Q

what are the measures to prevent TB?

A

–improved housing

–better nutrition

47
Q

BCG vaccine 100% prevents getting TB.

True/False

A

False.

Its main advantage is the prevention of severe diseases like Miliary TB.

48
Q

BCG vaccine is live or killed?

A
  • Bacilli-Calmette-Guerin (BCG) consists of a live attenuated strain of M. bovis
  • Produces a delayed-type hypersensitivity reaction similar to that of natural infection
  • Contraindicated in immunosuppressed patients & those who are skin test + ve
49
Q

Non-tuberculous mycobacteria are more pathogenic than MTB. True/False

A

False.
•Less pathogenic, often in the environment
•Not considered infectious

50
Q

factors that increase the prevalence of Non-tuberculous mycobacteria?

A

more awareness; other factors e.g. AIDS, solid organ transplantation

51
Q

which Non-tuberculous mycobacteria resemble MTB presentation?

A

M. Kansasii

52
Q

what inborn disease increases the risk of respiratory infection with non-tuberculous mycobacteria?

A

Cystic fibrosis

53
Q

what is the source of M. avium intracellulare complex? (MAC)

A

environment (soil/water)

54
Q

what disease predispose to MAC infection?

A

AIDS (CD4 T cell count <50)

55
Q

what drug is used for prophylaxis of MAC in AIDS patient with CD4 < 50

A

azithromycin

56
Q

small, round, raised erythematous papules on hand can be caused by what atypical mycobacteria?

A

M marinum

cause aquarium granuloma, which typically affects individuals who work with fish or keep home aquariums

57
Q

which bacteria never have been grown in vitro?

A

M. leprae.

•Historically, associated with disfigurement & led to ostracism

58
Q

M. leprae is found in what cells?:

1) macrophages
2) epithelial cells
3) Schwann cells
4) B lymphocytes

A

macrophages

59
Q

what cells are the primary target of M leprae?

A

Schwann cell the primary target leading to anesthesia; paralysis with granulomata

60
Q

what cells are the primary target of M leprae?

A

Schwann cell the primary target leading to anesthesia & paralysis with granulomata
other—skin lesions with or without pigmentation, disability, nasal destruction; eye lesions

61
Q

how to diagnose leprosy?

A

Diagnosis by tissue smears for acid-fast bacilli; histopathology

62
Q

name antibiotics used to treat leprosy.

A

Dapsone, rifampicin & clofazimine for 6-12 months or longer
Clofazimine (+ dapsone and rifampin) is used in multibacillary leprosy whereas only dapsone and rifampin in paucibacillary (tuberculoid) leprosy

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