Quiz 12: Mycobacteriology and Fastidious Gram-Negative Bacilli

This virulence factor is unique to M. tuberculosis (MTB)

Cording factor

This is the hallmark of tuberculosis

Tubercle formation

A 30yo healthcare provider working in a Baltimore City hospital is exposed to a patient diagnosed with TB. What form of TB would most likely occur in this healthcare provider?

Latent

A positive PPD indicates the patient most likely has

Been infected with MTB

In the IGRA blood test for the detection of MTB infection, what is being measured as the indicator of a positive response?

IFN-γ

CDC recommends that first-line treatment of pulmonary TB includes these anti-mycobacterials

Isoniazid and rifampin

Mycobacteriae are described as “acid-fast bacilli” because they

Are resistant to decolorizing with acid-alcohol

This is a non-selective, albumin based medium to isolate mycobacteriae

Middlebrook 7H10

Which Mycobacterium spp. does not produce the enzyme to convert niacin to nicotinic acid

M. tuberculosis

Which of these results is not consistent with the identification of M. tuberculosis?

LJ: Buff-colored colonies

Niacin accumulation: Yellow

Nitrate: Pink-red after reagents added

68C thermostable catalase: Bubbles

68C thermostable catalase: Bubbles

Which statement is true regarding molecular tests for mycobacteriae?

a. Digestion of sputum specimens is not required to perform PCR

b. NAAT are based on the amplification and detection of 16s rRNA

c. Species specific probes differentiate M. bovis and M. tuberculosis

d. Because they are highly sensitive, it’s not necessary to culture positive specimens

b. NAAT are based on the amplification and detection of 16s rRNA

Growth within 7 days after subculture

Rapid grower

Yellow pigment produced after exposed to light for 3-5hrs

Photochromagens

No pigment after exposed to light for 3-5hrs

Non-chromagens

Yellow pigment produced when grown in light or dark

Scotochromagen

Which statement is true about M. avium-intracellulare complex?

a. Used to prepare the BCG vaccine

b. Colonies appear on solid media within 7 days

c. Non-chromogen

d. Niacin accumulation test-positive

c. Non-chromogen

This Mycobacterium spp. produces yellow colonies only after exposure to 3-5hrs of incandescent light

M. kansasii

This species is known as the “tap-water scotochromogen”

M. gordonae

Culture of a hand wound from a manager of a tropical fish store grew AFB on MIiddlebrook agar @30C after 10 days incubation. On subculture, the isolate is found to be a photochromagen. This isolate is most likely:

M. marinum

A slow growing, yellow pigmented AFB isolated from a cervical lymph node of a child diagnosed with lymphadenitis is most likely

M. scrofulaceum

M. fortuitum grows on a subculture on L-J agar in 5 days. What other species is able to grow in the same time period?

M. chelonae

This disease is slow to progress, characterized by skin lesions and symmetric peripheral nerve damage, and may lead to destruction of the cartilage with facial deformities.

Lepromatous leprosy