Chapter 7.8 - Mycobacteria (HARR)

First morning specimen

The best specimen for recovery of the mycobacteria from a sputum sample is:

4% NaOH

What concentration of sodium hydroxide (NaOH) is used to prepare a working decontamination solution for the processing of not normally sterile specimens for mycobacteria?

Petragnani’s agar

Which is the most appropriate nonselective medium for recovery of mycobacteria from a heavily contaminated specimen?

Bright red rods against a blue background

Mycobacteria stained by the Ziehl–Neelsen or Kinyoun methods with methylene blue counterstain are seen microscopically as:

Mycobacterium tuberculosis

Acid-fast staining of a smear prepared from digested sputum showed slender, slightly curved, beaded, red mycobacterial rods. Growth on Middlebrook 7H10 slants produced buff-colored microcolonies with a serpentine pattern after 14 days at 37°C. Niacin and nitrate reduction tests were positive. What is the most probable presumptive identification?

Mycobacterium bovis

Which organism, associated with tuberculosis in cattle, causes tuberculosis in humans, especially in regions where dairy farming is prevalent?

Mycobacterium fortuitum and Mycobacterium tuberculosis

Which of the following organisms are used as controls for rapid growers and slow growers?

Mycobacterium kansasii

All of the following mycobacteria are associated with skin infections except:

Mycobacterium tuberculosis

All of the following Mycobacterium spp. produce the enzyme required to convert niacin to niacin ribonucleotide except:

30% H2O2 and 10% Tween 80

The catalase test for mycobacteria differs from that used for other types of bacteria by using:

M. bovis

Growth inhibition by thiophene-2-carboxylic hydrazide (T2H) is used to differentiate M. tuberculosis from which other Mycobacterium specie?

M. kansasii

Which of the following Mycobacterium spp. is best differentiated by the rapid hydrolysis of Tween 80?

Mycobacterium xenopi

Mycobacteria isolated from the hot water system of a hospital grew at 42°C. Colonies on Löwenstein–Jensen medium were not pigmented after exposure to light and were negative for niacin accumulation and nitrate reduction. The most likely identification is:

M. gordonae

The urease test is needed to differentiate Mycobacterium scrofulaceum from which of the following mycobacteria?

Acid-fast staining, inoculation, and referral to a reference laboratory

According to the College of American Pathologists (CAP) guidelines, which services for mycobacteria would be performed by a Level II laboratory?

M. gordonae

Which nonpathogenic Mycobacterium specie is isolated most often from clinical specimens and is called the “tapwater bacillus”?

Isonicotinic acid hydrazide (INH), rifampin, ethambutol, and pyrazinamide

Which of the following drugs are first-line antibiotics used to treat classic tuberculosis for which susceptibility testing is performed by the disk diffusion method on Middlebrook 7H10 or 7H11 agar plates?

6–12 months

How long should Mycobacterium tuberculosis–positive cultures be kept by the laboratory after identification and antibiotic susceptibility testing have been performed?

Numerous or 3+

According to the reporting standards of the American Thoracic Society, one or more acid-fast bacilli (AFB) per oil immersion field (1,000×) are reported as:

M. chelonae–fortuitum complex

Which of the following Mycobacterium spp. would be most likely to grow on a MacConkey agar plate?

All of these options:

• Gas–liquid chromatography

• Nucleic acid probes

• Acid-fast smears

Rapid methods for identifying classic infection with M. tuberculosis include:

Latently infected

Individuals showing a positive purified protein derivative (PPD) skin test for M. tuberculosis are usually:

M. leprae

Which of the following Mycobacterium species is diagnosed by means other than culture?

M. avium

Which M. avium complex (MAC) organism is the most frequently isolated mycobacterium from AIDS patients?

M. microti

Which mycobacterium of the M. tuberculosis complex fails to grow in culture and has a characteristic “croissant-like” morphology in stained smears?

M. haemophilum and M. ulcerans

Which two mycobacteria commonly isolated from subcutaneous skin have an optimal growth temperature of 30°C?

M. paratuberculosis

Which mycobacterium is associated with Crohn’s disease?

30°C–32°C

Which temperature range is ideal for the recovery of M. marinum?