Mycobacteriology Flashcards Preview

Liz's Microbiology Module 2 > Mycobacteriology > Flashcards

Flashcards in Mycobacteriology Deck (113):
1

Why do acid-fast bacteria stain acid fast?

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

2

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

Mycobacterial culture contamination rate of 3-5% is tolerable
- < 3% → overly harsh decontamination
- > 5% → insufficient contamination

3

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

M. tuberculosis complex

4

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

Rifampin resistance

5

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

Egg and agar

6

Give examples of egg-based media

- Lowentstein-Jensen
- American Trudeau Society

7

Give examples of agar-based media

- Middlebrook 7H10
- Middlebrook 7H11

8

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

- MGIT
- Bactec Alert

9

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

Broth

10

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

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

11

Scotochromogen

Produces pigments independent of light exposure

12

Photochromogen

Produces pigments only after exposure to light

13

Nonchromogen

Never produces a pigment

14

Rapid grower

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

15

Slow grower

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

16

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

Middlebrook 7H9

17

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

- M. avium
- M. genavense
- M. kansasii
- M. gordonae (common contaminant)

18

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

Acid-fast
- Gordonia spp (weakly-positive)
- Nocardia spp (positive, beaded appearance)
- Rhodococcus spp (weakly-positive)
- Segniliparus spp (strongly-positive)
- Tsukamurella spp (weakly-positive)

19

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

Mycobacteria are stained red; background is blue

20

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

BCG

21

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

- M. tuberculosis
- M. leporae

22

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

- Skin cultures are incubated at 30C

23

ALL cultures are set up on what media?

Solid and broth media

24

Outline the specimen collection recommendations for respiratory mycobacteria cultures

3 separate specimens must be collected at least 8 hours apart

25

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

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

26

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

Auramine-Rhodamine

27

What is the most common submitted specimen for TB diagnosis?

Sputum

28

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

Crap concentrates in the lungs throughout the night

29

Define incubation times and conditions for mycobacterial cultures

- 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

30

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

6-8 weeks

31

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

4 weeks

32

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

8-12 weeks

33

Cultures should be examined how many days after inoculation?

3-5 days

34

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

Twice per week

35

After 4 weeks, cultures should be examined how often?

Once per week until 6-8 weeks

36

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

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

37

Which mycobacteria are inhibied by T2H?

M. bovis

38

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

- M. abscessus/chelonae
- M. fortuitum
- M. haemophilum
- M. ulcerans
- M. marinum

39

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

- M. tuberculosis complex (M. tuberculosis, bovis, africanum)
- M. avium
- M. fortuitum
- M. kansasii
- M. szulgai
- M. scrofulaceum

40

List the mycobacteria that grow at 42C and 45C

- M. xenopi (42°C)
- M. thermoresistable (45°C)

41

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

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

42

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

M. genavense requires mycobactin J
- VERY fastidious

43

List the slow growing mycobacteria

- M. avium
- M. genavense
- M. gordonae
- M. haemophilum
- M. kansasii
- M. marinum
- M. scrofulcaneum
- M. szulgai
- M. tuberculosis complex
- M. ulcerans
- M. xenopi

44

Describe the appearance of M. tuberculosis on agar

ROUGH, wrinkled, waxy, BUFF-colored

45

Describe the appearance of M. kansasii on agar

Rough, wrinkled

46

Describe the appearance of M. xenopi on agar

Smooth and yellow-colored

47

Describe the appearance of M. fortuitum on agar

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

48

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

- M. tuberculosis complex
- M. avium-intracellulare complex
- M. gordonae
- M. kansasii

49

Which species of mycobacteria are commonly implicated in scorula?

- M. avium complex (#1)
- M. scrofulaceum (until 1980s)

50

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

M. avium complex
- M. avium
- M. intracellulare
- M. chimaera

51

Which tests distinguish M. tuberculosis and M. bovis

- Nitrate reduction
- T2H
- Pyrazinminidase (PZA)

52

List examples of scotochromogens

- M. gordonae
- M. scrofulaceum
- M. szulgai (@ 37C)
- M. xenopi

53

List examples of photochromogens

- M. kansasii
- M. marinum
- M. szulgai (@ 25°C)

54

List examples of nonchromogens

- M. abcessus/chelonae
- M. avium
- M. fortuitum
- M. haemophilum
- M. tuberculosis

55

List the rapid growing mycobacteria

- M. abscessus/chelonae
- M. fortuitum
- M. smegmatis

56

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

Arylsulfatase

57

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

Urease

58

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

Pyrazinamidase
- M. tuberculosis (+)
- M. bovis (-)
- M. marinum (+)
- M. kansasii (-)

59

Describe the utility of the pyrazinamidase test

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

60

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

Iron uptake test

61

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

M. abscessus

62

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

M. tuberculosis complex
- M. tuberculosis
- M. bovis
- M. africanum

63

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

Rifampin resistance (and isoniazid resistance is predicted from this)

64

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

Direct patient sputum

65

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

Mycolic acid from mycobacterial cell wall

66

List the two most common causes of NTM lung disease

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

67

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

- Fresh-water fish tanks
- Salt water

68

What disease is caused by M. ulcerans

Buruli ulcer (aka Brainsdale ulcer)

69

What disease is caused by M. leprae?

Leprosy

70

Nitrate reduction
- Media

Potassium nitrate

71

Nitrate reduction
- Reagents

- Alpha-naphthylamine or dimethyl-alpha-napthylamine
- Sulfonilic acid
- Zinc dust

72

Nitrate reduction
- Positive test
- Negative test

- Pos: Red
- Neg: Colorless

73

Niacin
- Positive test
- Negative test

- Pos: yellow
- Neg: white/clear

74

Tween 80 hydrolysis
- Positive test
- Negative test

- Pos: red (nonpathogenic)
- Neg: yellow/orange (pathogenic)

75

Heat-stable catalase
- Positive test
- Negative test

- Pos: bubbles
- Neg: no bubbles

76

Arylsulfatase
- Positive test
- Negative test

- Pos: red
- Neg: clear

77

Urease
- Positive test
- Negative test

- Pos: pink
- Neg: yellow

78

Pyrazinaminidase
- Positive test
- Negative test

- Pos: pink
- Neg: no pink top layer

79

Iron uptake
- Positive test
- Negative test

- Pos: brownish slant
- Neg: not brown

80

T2H
- Positive test
- Negative test

- Pos: growth
- Neg: no growth

81

5% NaCl
- Positive test
- Negative test

- Pos: growth > 50 colonies
- Neg: no growth < 50 colonies

82

MAC w/o Crystal Violet
- Positive test
- Negative test

- Pos: growth
- Neg: no growth

83

Tellurite reduction
- Positive test
- Negative test

- Pos: gray/clear
- Neg: yellow

84

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

- Rifampin
- Isoniazid
- Pyrazinamide
- Ethambutol
- Streptomycin

85

List infections associated w/ rapidly-growing mycobacteria

- Post-traumatic wound infections

86

Define drug-resistant TB

Resistant to rifampin and isoniazid

87

Define multi-drug resistant TB

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

88

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

Method of Proportion (MOP)

89

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

- Broth microdilution
- Disk or strip diffusion (Etest)

90

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

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

91

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

Delayed-type hypersensitivity

92

TB skin test
- False positives

- Previous BCG vaccination (vaccination w/ M. bovis BCG)
- Incorrect method of TST administration
- Infection w/ some NTM

93

TB skin test
- False negatives

- 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

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

3 tubes are collected
- Red, purple, grey

95

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

Grey; Ags

96

Which QuantiFERON tube is the "test" tube?

Red

97

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

Purple; interferon-gamma release

98

QuantiFERON Gold In-Tube test
- False positive

Infection w/ some NTM

99

QuantiFERON Gold In-Tube test
- False negative

- Dysfunctional immune ells of lymphocytopenia
- Positive control will also be negative

100

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

- Capreomycin
- Ciprofloxacin (Cipro)
- Cycloserine
- Doxycycline or minocycline
- Kanamycin
- Rifabutin
- Trimethoprim-sulfamethoxazole

101

Which mycobacteria are POSITIVE for arylsulfatase?

- M. abscessus
- M. africanum
- M. fortuitum

102

Which mycobacteria are POSITIVE for niacin?

M. tuberculosis

103

Which mycobacteria are POSITIVE for nitrate?

- M. fortuitum
- M. kansasii
- M. szulgai
- M. tuberculosis

104

Which mycobacteria are NEGATIVE for urease?

- M. africanum
- M. avium
- M. gordonae
- M. haemophilum
- M. ulcerans
- M. xenopi

105

Which mycobacteria are NEGATIVE for PZA?

- M. africanum
- M. bovis
- M. gordonae
- M. kansasii
- M. scrofulaceum
- M. szulgai
- M. ulcerans

106

Which mycobacteria are NEGATIVE T2H?

M. bovis

107

Which mycobacteria are POSITIVE for Tween 80 hydrolysis?

- M. genavense
- M. gordonae
- M. kansasii
- M. marinum

108

Which mycobacteria are POSITIVE for 68°C catalase?

- M. abscessus
- M. chelonae
- M. fortuitum
- M. genavense
- M. gordonae
- M. kansasii
- M. marinum

109

Which mycobacteria grow in the presence of 5% NaCl?

- M. abscessus
- M. fortuitum

110

Which mycobacterium is POSITIVE for iron uptake?

M. fortuitum

111

Which mycobacteria grow on MAC w/o crystal violet?

- M. abscessus
- M. fortuitum

112

Which mycobacteria are associated with soil?

Rapid growers
- M. gordonae

113

Describe microscopic examination of fluorescent stains

A minimum of 30 fields using 250x magnification