Mycobacteriology Part II

Question 1

Objective 1: Identify positive and negative results for the Niacin and Nitrate tests

Answer 1

Niacin:
- Positive: Yellow
- Negative: No color change

Nitrate:
- Positive: Red
- Negative: No color change or pink color color after the addition of zinc

Question 2

Objective 2: Discuss the organisms that are differentiated using the pyrazinamidase test

Answer 2

M. tuberculosis (+) from M. bovis (-)
M. avium complex (+)

Question 3

Objective 3: Discuss the utility of the pyrazinamidase test (How might treatment of a patient be affected by results?)

Answer 3

Pyrazinamide (PZA) is an antimicrobial used to treat mycobacterium infections, but is ONLY effective against organisms that can convert PZA to pyrazinoic acid – if an organism can not perform this, it will be drug-resistant to PZA

Question 4

Objective 4: Discuss the Xpert MTB/RIF real time PCR test. Include the 3 main organisms which are detected, the antibiotic resistance gene that is detected, and whether the test is performed on culture or direct patient specimen

Answer 4

1. M. tuberculosis
2. M. bovis
3. M. africanum

• Detects rifampin resistance
• Performed on direct patient specimen

Question 5

Objective 5: Explain why the DNA probe (Hybridization) assays used for identification of
mycobacteria target ribosomal RNA and not chromosomal DNA

Answer 5

Makes testing system more sensitive — there are exponentially more RNA copies than DNA copies per bacterium

Question 6

Objective 6: List the 4 DNA probe assays that are currently available for Mycobacterium speciation

Answer 6

1. M. tuberculosis complex
2. M. avium complex
3. M. kansasii
4. M. gordonae

Question 7

Objective 7: List 2 additional requirements for the processing of Mycobacterium spp. for MALDI-TOF MS

Answer 7

1. Inactivation step to ensure safety
2. Additional extraction requirements

Question 8

Objective 8: Recognize the component of mycobacteria which is analyzed using high-
performance liquid chromatography (HPLC)

Answer 8

Mycolic acids

Question 9

Objective 10: Describe the appearance of these mycobacteria on agar plates:
- M. tuberculosis

Answer 9

ROUGH, wrinkled, waxy, BUFF-colored

Question 10

Objective 11: List tests that distinguish M. tuberculosis from M. bovis and their expected reactions

Answer 10

M. tuberculosis:
- Niacin (+)
- Nitrate (+)
- PZA (+ or Susc.)

M. bovis:
- Niacin (V/-)
- Nitrate (-)
- PZA (- or Resist.)

Question 11

Objective 12: Recognize the factor/characteristic that when visualized microscopically is highly suggestive of M. tuberculosis and indicates virulence

Answer 11

Cording factor — serpentine arrangement

Question 12

Objective 13: Recognize the species of mycobacteria historically associated with AIDS patients and that are isolatable from stool and blood

Answer 12

Mycobacterium avium complex (MAC):
- M. avium (multiple subspecies)
- M. intracellulare
- M. chimaera

Question 13

Objective 14: List the special requirements for isolation of M. haemophilum

Answer 13

• Choc. agar
• Growth at 30-32 deg. C

Question 14

Objective 16: Recognize the disease caused by M. ulcerans

Answer 14

“Buruli ulcer” or “Bairnsdale ulcer”

Question 15

Objective 10: Describe the appearance of these mycobacteria on agar plates:
- M. kansasii

Answer 15

Rough, wrinkled, yellow when exposed to light (photochromogen)

Question 16

Objective 15: List the 2 most common causes of NTM lung disease

Answer 16

1. Mycobacterium avium complex
2. M. kansasii

Question 17

Objective 17: Describe the unique microscopic appearance of M. kansasii when stained with a
Carbolfuchsin stain

Answer 17

Cross-banding “candy cane”

Question 18

Objective 18: Discuss the most common type of infection and route of transmission associated
with M. marinum

Answer 18

Cutaneous lesions/ulcers as a result of trauma and exposure of open wounds to fresh water fish tanks or salt water

Question 19

Objective 19: Recognize the Mycobacterium species which is generally nonpathogenic, is a common contaminant in the AFB lab, and may be isolated from tapwater

Answer 19

M. gordonae

Question 20

Objective 10: Describe the appearance of these mycobacteria on agar plates:
- M. xenopi

Answer 20

“Bird nest” appearance

Question 21

Objective 20: Recognize the species of mycobacteria that are commonly implicated in scrofula

Answer 21

M. scrofulaceum

Question 22

Objective 21: Recognize the organism that is a scotochromogen at 37°C, but a photochromogen at lower temperatures

Answer 22

M. szulgai

Question 23

Objective 22: Select the appropriate incubation conditions for M. xenopi

Answer 23

42 deg. C

Question 24

Objective 10: Describe the appearance of these mycobacteria on agar plates:
- M. fortuitum

Answer 24

Umbonate — raised center with dry flat skirt growth

Question 25

Objective 23: List infections associated with rapidly-growing mycobacteria

Answer 25

• Post traumatic wound infections
• Bone/joint infections
• Corneal infections
• Pulmonary infections
• Disseminated cutaneous diseases

Question 26

Objective 24: List optimal growth temperatures for each of the rapidly-growing mycobacteria

Answer 26

M. chelonae: ~ 30 deg. C
M. abscessus & M. fortuitum: 35-37 deg. C

Question 27

Objective 25: Identify the rapidly-growing mycobacteria that is associated with cystic fibrosis
patients

Answer 27

M. abscessus

Question 28

Objective 26: Define extensively drug-resistant TB and multi-drug resistant TB

Answer 28

Multi-drug resistant TB:
- Resistant to rifampin and isoniazid

Extensively drug-resistant TB:
- Resistant to rifampin, isoniazid, quinolones, etc.

Question 29

Objective 27: List “first line” antibiotics used to treat infections caused by MTB complex organisms

Answer 29

“RIPE” Therapy
Rifampin
Isoniazid
Pyrazinamide (PZA)
Ethambutol
(Streptomycin)