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Liz's Microbiology Module 2 > Mycobacteriology > Flashcards

Mycobacteriology Flashcards

1
Q

Why do acid-fast bacteria stain acid fast?

A

Cell walls contain mycolic acid (long-chain fatty acids)

  • When stained w/ special dye, cells can’t be decolorized w/ weak-acid-alcohol solution
  • Acid-fast organisms stain red
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2
Q

What is the “ideal” contamination rate that mycobacteria labs should strive for when assessing their decontamination rate?

A

Mycobacterial culture contamination rate of 3-5% is tolerable

  • < 3% → overly harsh decontamination
  • > 5% → insufficient contamination
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3
Q

Which mycobacterium species are identified on the GeneXpert (Xpert MTB/RIF) system?

A

M. tuberculosis complex

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4
Q

What antimicrobial susceptiblity are identified on the GeneXpert (Xpert MTB/RIF) system?

A

Rifampin resistance

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5
Q

What two categories of solid media are used for the isolation of mycobacteria

A

Egg and agar

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6
Q

Give examples of egg-based media

A
  • Lowentstein-Jensen

- American Trudeau Society

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7
Q

Give examples of agar-based media

A
  • Middlebrook 7H10

- Middlebrook 7H11

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8
Q

What two types of broth media are used for the isolation of mycobacteria?

A
  • MGIT

- Bactec Alert

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9
Q

Which type media, solid or broth, is able to recover organisms more quickly?

A

Broth

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10
Q

How do you set up a skin culture for mycobacteria, including temperature, media, etc.

A

Set up 7H10 @ 37C and 30C and set up MGIT @ 37C

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11
Q

Scotochromogen

A

Produces pigments independent of light exposure

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12
Q

Photochromogen

A

Produces pigments only after exposure to light

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13
Q

Nonchromogen

A

Never produces a pigment

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14
Q

Rapid grower

A

Requires < 7 days to produce colonies when subculutred onto certain media

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15
Q

Slow grower

A

Requires > 7 days to produce colonies on solid media under ideal culture conditions

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16
Q

What broth medium is used in MGIT, Bact/ALERT, and BACTEC Myco/F Lytic system?

A

Middlebrook 7H9

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17
Q

Which mycobacteria are nonpathogenic and may be isolated from tap water?

A
  • M. avium
  • M. genavense
  • M. kansasii
  • M. gordonae (common contaminant)
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18
Q

Which mycobacteria are acid-fast and modified acid-fast?

A

Acid-fast

  • Gordonia spp (weakly-positive)
  • Nocardia spp (positive, beaded appearance)
  • Rhodococcus spp (weakly-positive)
  • Segniliparus spp (strongly-positive)
  • Tsukamurella spp (weakly-positive)
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19
Q

What do mycobacteria and the background look like when using the Ziehl-Neelsen or Kinyoun methods?

A

Mycobacteria are stained red; background is blue

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20
Q

List the strain of M. bovis which is used to produce the M. tuberculosis vaccine

A

BCG

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21
Q

List the species of Mycobacteria which cannot be cultured in the lab routinely (requires living cells)

A
  • M. tuberculosis

- M. leporae

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22
Q

Differentiate the temperature(s) at which plates are incubated for skin cultures and sputum (respiratory) cultures

A
  • Skin cultures are incubated at 30C
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23
Q

ALL cultures are set up on what media?

A

Solid and broth media

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24
Q

Outline the specimen collection recommendations for respiratory mycobacteria cultures

A

3 separate specimens must be collected at least 8 hours apart

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25
Q

What biosafety level and lab containment mechanisms are required for working w/ mycobacterial cultures?

A

BSL-3

  • Floor, wall, and ceiling surfaces are sealed and coated w/ an epoxy for ease of disinfection
  • Air is drawn from the outside of the lab INTO the lab (negative air pressure)
  • All work w/ clinical specimens and cultures is conducted in biological safety cabinets
  • Separated from BSL-2 lab space by at least 2 doors
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26
Q

____ stain is the best choice for screening patients and is specific for acid-fast organisms

A

Auramine-Rhodamine

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27
Q

What is the most common submitted specimen for TB diagnosis?

A

Sputum

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28
Q

Why must one of the sputum specimens be collected in the morning?

A

Crap concentrates in the lungs throughout the night

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29
Q

Define incubation times and conditions for mycobacterial cultures

A
  • Broths are incubated w/in a continuous monitoring system
  • Agar- and egg-based media are incubated in 5-10% CO2
  • MTB and most other mycobacteria incubated at 35-37C
  • Skin specimens incubated at 30C
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30
Q

How long should cultures be incubated before being reported as negative?

A

6-8 weeks

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31
Q

If specimens are smear-positive but don’t grow in 6-8 weeks, add how many more weeks onto the incubation duration?

A

4 weeks

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32
Q

Specimens from skin should be incubated for how many weeks if M. ulcerans is suspected?

A

8-12 weeks

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33
Q

Cultures should be examined how many days after inoculation?

A

3-5 days

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34
Q

How often should cultures be examined for the first 4 weeks?

A

Twice per week

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35
Q

After 4 weeks, cultures should be examined how often?

A

Once per week until 6-8 weeks

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36
Q

Why does the DNA probe used to identify M. tuberculosis target rRNA and not chromosomal DNA?

A

This makes the assay more sensitive since there are 10,000 copies of RNA per bacterium and only 1-2 copies of DNA; if the DNA probe binds to target RNA molecules, the DNA-RNA hybrid can be detected by chemilumescence

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37
Q

Which mycobacteria are inhibied by T2H?

A

M. bovis

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38
Q

List the mycobacteria that grow optimally at 30°C (6)

A
  • M. abscessus/chelonae
  • M. fortuitum
  • M. haemophilum
  • M. ulcerans
  • M. marinum
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39
Q

List the mycobacteria that grow optimally at 35-37°C (5)

A
  • M. tuberculosis complex (M. tuberculosis, bovis, africanum)
  • M. avium
  • M. fortuitum
  • M. kansasii
  • M. szulgai
  • M. scrofulaceum
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40
Q

List the mycobacteria that grow at 42C and 45C

A
  • M. xenopi (42°C)

- M. thermoresistable (45°C)

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41
Q

What are the special requirements for isolation of M. haemophilum?

A

M. haemophilum requires hemin (X factor in CHOC agar)

- Fastidious

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42
Q

What are the special requirements for isolation of M. genavense?

A

M. genavense requires mycobactin J

- VERY fastidious

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43
Q

List the slow growing mycobacteria

A
  • M. avium
  • M. genavense
  • M. gordonae
  • M. haemophilum
  • M. kansasii
  • M. marinum
  • M. scrofulcaneum
  • M. szulgai
  • M. tuberculosis complex
  • M. ulcerans
  • M. xenopi
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44
Q

Describe the appearance of M. tuberculosis on agar

A

ROUGH, wrinkled, waxy, BUFF-colored

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45
Q

Describe the appearance of M. kansasii on agar

A

Rough, wrinkled

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46
Q

Describe the appearance of M. xenopi on agar

A

Smooth and yellow-colored

47
Q

Describe the appearance of M. fortuitum on agar

A

Umbonate (raised center) colonies surrounded by a flat, dry skirt of growth

48
Q

DNA probe assays that are currently available for which 4 Mycobacteria species?

A
  • M. tuberculosis complex
  • M. avium-intracellulare complex
  • M. gordonae
  • M. kansasii
49
Q

Which species of mycobacteria are commonly implicated in scorula?

A
  • M. avium complex (#1)

- M. scrofulaceum (until 1980s)

50
Q

Which species of mycobacteria are historically associated w/ AIDS patients and that are isolatable from stool and blood?

A

M. avium complex

  • M. avium
  • M. intracellulare
  • M. chimaera
51
Q

Which tests distinguish M. tuberculosis and M. bovis

A
  • Nitrate reduction
  • T2H
  • Pyrazinminidase (PZA)
52
Q

List examples of scotochromogens

A
  • M. gordonae
  • M. scrofulaceum
  • M. szulgai (@ 37C)
  • M. xenopi
53
Q

List examples of photochromogens

A
  • M. kansasii
  • M. marinum
  • M. szulgai (@ 25°C)
54
Q

List examples of nonchromogens

A
  • M. abcessus/chelonae
  • M. avium
  • M. fortuitum
  • M. haemophilum
  • M. tuberculosis
55
Q

List the rapid growing mycobacteria

A
  • M. abscessus/chelonae
  • M. fortuitum
  • M. smegmatis
56
Q

Which biochemical test which allows differentiation of rapid growers from slow-growing nonchromogenic mycobacteria?

A

Arylsulfatase

57
Q

Which biochemical test is used to distinguish M. scrofulaceum from M. gordonae?

A

Urease

58
Q

Which test is used to distinguish M. tuberculosis from M. bovis and M. marinum from M. kansasii

A

Pyrazinamidase

  • M. tuberculosis (+)
  • M. bovis (-)
  • M. marinum (+)
  • M. kansasii (-)
59
Q

Describe the utility of the pyrazinamidase test

A

Pyrazinamidase is an enzyme that converts the drug pyrazinamide to pyrazinoic acid

60
Q

Which biochemical test helps distinguish M. fortuitum from M. abscessus/chelonae?

A

Iron uptake test

61
Q

Which rapid-growing mycobacteria can grow in the presence of 5% NaCl?

A

M. abscessus

62
Q

Which organisms are detected by the Xpert MTB/RIF real time PCR test

A

M. tuberculosis complex

  • M. tuberculosis
  • M. bovis
  • M. africanum
63
Q

Which antibiotic resistance gene is detected w/ the Xpert MTB/RIF real time PCR test?

A

Rifampin resistance (and isoniazid resistance is predicted from this)

64
Q

Is the Xpert MTB/RIF real time PCR test performed on culture or direct patient specimen?

A

Direct patient sputum

65
Q

What component of mycobacteria is analyzed using high performance liquid chromatography (HPLC)?

A

Mycolic acid from mycobacterial cell wall

66
Q

List the two most common causes of NTM lung disease

A 
M. avium complex (#1 cause)
- M. avium
- M. intracellulare
- M. chimaera
M. kansasii (#2 cause)
67
Q

What is the common route of infection associated w/ M. marinum?

A
  • Fresh-water fish tanks

- Salt water

68
Q

What disease is caused by M. ulcerans

A

Buruli ulcer (aka Brainsdale ulcer)

69
Q

What disease is caused by M. leprae?

A

Leprosy

70
Q

Nitrate reduction

- Media

A

Potassium nitrate

71
Q

Nitrate reduction

- Reagents

A
  • Alpha-naphthylamine or dimethyl-alpha-napthylamine
  • Sulfonilic acid
  • Zinc dust
72
Q

Nitrate reduction

  • Positive test
  • Negative test
A
  • Pos: Red

- Neg: Colorless

73
Q

Niacin

  • Positive test
  • Negative test
A
  • Pos: yellow

- Neg: white/clear

74
Q

Tween 80 hydrolysis

  • Positive test
  • Negative test
A
  • Pos: red (nonpathogenic)

- Neg: yellow/orange (pathogenic)

75
Q

Heat-stable catalase

  • Positive test
  • Negative test
A
  • Pos: bubbles

- Neg: no bubbles

76
Q

Arylsulfatase

  • Positive test
  • Negative test
A
  • Pos: red

- Neg: clear

77
Q

Urease

  • Positive test
  • Negative test
A
  • Pos: pink

- Neg: yellow

78
Q

Pyrazinaminidase

  • Positive test
  • Negative test
A
  • Pos: pink

- Neg: no pink top layer

79
Q

Iron uptake

  • Positive test
  • Negative test
A
  • Pos: brownish slant

- Neg: not brown

80
Q

T2H

  • Positive test
  • Negative test
A
  • Pos: growth

- Neg: no growth

81
Q

5% NaCl

  • Positive test
  • Negative test
A
  • Pos: growth > 50 colonies

- Neg: no growth < 50 colonies

82
Q

MAC w/o Crystal Violet

  • Positive test
  • Negative test
A
  • Pos: growth

- Neg: no growth

83
Q

Tellurite reduction

  • Positive test
  • Negative test
A
  • Pos: gray/clear

- Neg: yellow

84
Q

List the “first-line” antibiotics used to treat infections caused by MTB complex organisms

A
  • Rifampin
  • Isoniazid
  • Pyrazinamide
  • Ethambutol
  • Streptomycin
85
Q

List infections associated w/ rapidly-growing mycobacteria

A
  • Post-traumatic wound infections
86
Q

Define drug-resistant TB

A

Resistant to rifampin and isoniazid

87
Q

Define multi-drug resistant TB

A

Resistant to rifampin, isoniazid, quinolones (e.g., ciprofloxacin), and other drugs

88
Q

What standard method is used for testing MTB against almost all antimicrobials (except pyrazinamide)?

A

Method of Proportion (MOP)

89
Q

What 2 testing methods are used for antimicrobial susceptibility testing of NTM mycobacteria?

A
  • Broth microdilution

- Disk or strip diffusion (Etest)

90
Q

Describe the administration method of the TB skin test (TST)

A

Purified proteins (tuberculin) from MTB cells are injected intradermally on the inner forearm

91
Q

If a person has been exposed to TB bacteria, a ____ ____ reaction occurs

A

Delayed-type hypersensitivity

92
Q

TB skin test

- False positives

A
  • Previous BCG vaccination (vaccination w/ M. bovis BCG)
  • Incorrect method of TST administration
  • Infection w/ some NTM
93
Q

TB skin test

- False negatives

A
  • Very recent TB infection (w/in 8-10 weeks of exposure)
  • Very old TB infection (many years ago)
  • Recent vaccination against measles or smallpox
  • Incorrect administration or interpretation of the TST
94
Q

How many tubes are collected for the QuantiFERON Gold In-Tube test?

A

3 tubes are collected

- Red, purple, grey

95
Q

Which QuantiFERON tube is the negative control and does NOT contain ____

A

Grey; Ags

96
Q

Which QuantiFERON tube is the “test” tube?

A

Red

97
Q

Which QuantiFERON tube is the positive control and contains a substance that elicits ____

A

Purple; interferon-gamma release

98
Q

QuantiFERON Gold In-Tube test

- False positive

A

Infection w/ some NTM

99
Q

QuantiFERON Gold In-Tube test

- False negative

A
  • Dysfunctional immune ells of lymphocytopenia

- Positive control will also be negative

100
Q

List the secondary antibiotics used to treat infections caused by MTB complex organisms

A
  • Capreomycin
  • Ciprofloxacin (Cipro)
  • Cycloserine
  • Doxycycline or minocycline
  • Kanamycin
  • Rifabutin
  • Trimethoprim-sulfamethoxazole
101
Q

Which mycobacteria are POSITIVE for arylsulfatase?

A
  • M. abscessus
  • M. africanum
  • M. fortuitum
102
Q

Which mycobacteria are POSITIVE for niacin?

A

M. tuberculosis

103
Q

Which mycobacteria are POSITIVE for nitrate?

A
  • M. fortuitum
  • M. kansasii
  • M. szulgai
  • M. tuberculosis
104
Q

Which mycobacteria are NEGATIVE for urease?

A
  • M. africanum
  • M. avium
  • M. gordonae
  • M. haemophilum
  • M. ulcerans
  • M. xenopi
105
Q

Which mycobacteria are NEGATIVE for PZA?

A
  • M. africanum
  • M. bovis
  • M. gordonae
  • M. kansasii
  • M. scrofulaceum
  • M. szulgai
  • M. ulcerans
106
Q

Which mycobacteria are NEGATIVE T2H?

A

M. bovis

107
Q

Which mycobacteria are POSITIVE for Tween 80 hydrolysis?

A
  • M. genavense
  • M. gordonae
  • M. kansasii
  • M. marinum
108
Q

Which mycobacteria are POSITIVE for 68°C catalase?

A
  • M. abscessus
  • M. chelonae
  • M. fortuitum
  • M. genavense
  • M. gordonae
  • M. kansasii
  • M. marinum
109
Q

Which mycobacteria grow in the presence of 5% NaCl?

A
  • M. abscessus

- M. fortuitum

110
Q

Which mycobacterium is POSITIVE for iron uptake?

A

M. fortuitum

111
Q

Which mycobacteria grow on MAC w/o crystal violet?

A
  • M. abscessus

- M. fortuitum

112
Q

Which mycobacteria are associated with soil?

A

Rapid growers

- M. gordonae

113
Q

Describe microscopic examination of fluorescent stains

A

A minimum of 30 fields using 250x magnification

Liz's Microbiology Module 2 (11 decks)

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