Sunday, January 4, 2015

Mycobacteriology Review Questions

1.  A 18 year old foreign exchange student has a positive tuberculin (PPD) skin test.  He had received a BCG vaccination as a child.  A whole cell mitogen assay for M. tuberculosis was performed and was reported negative.  This indicates which of the following:

a.  He has active tuberculosis
b.  He most likely has a non-tuberculosis mycobacteria infection
c.  He has a positive skin test most likely due to his BCG vaccine
d.  The whole cell mitogen assay is falsely negative
e.  Both tests should be repeated because they should always agree in reactivity

2.  Concentration and decontamination of respiratory specimens is necessary for processing of mycobacteria cultures.  Which of the following is not a correct statement?

a.  4% NaOH is a common treatment used to decontaminate specimens
b.  Oxalic acid is commonly used to decontaminate specimens that may contain a mucoid strain of Pseudomonas aeruginosa
c.  The speed of centrifugation is an important step for determining the sensitivity of stains and culture
d.  One concentrated sputum specimen is all that is necessary for ruling out tuberculosis
e.  Decontamination of respiratory specimens is based on raising the pH of the specimen to kill off contaminating bacteria

3.  A 62 year old homeless man began coughing up sputum streaked with blood.  Concentrated AFB stains revealed the presence of numerous Acid Fast Bacilli, moderate length and sticking together.  Which is the correct statement:

a.  The morphology of the organism in the AFB smear is consistent with Mycobacterium tuberculosis
b.  A real time PCR assay could be performed on the expectorated sputum specimen to assist in confirming a diagnosis of M. tuberculosis
c.  The sticking together of the organisms is consistent with M. tuberculosis producing cord factor
d.  The PPD and whole cell mitogen assay on this patient should both be positive
e.  All of the above

4.  A 40 year old male with HIV/AIDS develops a gradual onset of fatigue and anorexia.  The causative organism grew in AFB culture after 14 days, smooth colony, with an AFB stain positive for bacilli variable in size, but mostly small rods.  The AFB in culture was a non-photochromogen, biochemically inert, making molecular identification necessary.  The most likely organism causing this infection is:

a.  Mycobacterium tuberculosis
b.  Mycobacterium avium-intracelullare complex
c.  Mycobacterium fortuitum
d.  Mycobacterium kansasii
e.  Mycobacterium marinum

5.  A 60 year old male with chronic pulmonary disease develops a cough with the production of a small amount of blood tinged sputum.  An expectorated sputum specimen was collected.  The specimen grew from AFB culture a photochromagen, Niacin negative, Nitrate positive, 68 *C catalase positive, and the  organisms in the AFB stain were in the shape of a Shepherd’s crook.  The organism is most likely:

a.  Mycobacterium tuberculosis
b.  Mycobacterium xenopi
c.  Mycobacterium scrofulaceum
d.  Mycobacterium kansasii
e.  Mycobacterium szulgai

6.  A 30 year old female developed a tender red subcutaneous nodule on her hand following the cleaning of a salt water fish tank.  During the cleaning she scraped her hand on rocks in the bottom of the tank.  A biopsy from the lesion was cultured.  The organism did not grow at 37*C  (8% CO2)but grew an AFB identified to be a photochromagen at 30*C (8% CO2)   The organisms is most likely:

a.  Mycobacterium ulcerans
b.  Mycobacterium marinum
c.  Mycobacterium kansasii
d.  Mycobacterium fortuitum
e.  Mycobacterium chelonae complex

7.  A HIV/AIDS patient developed a cough and low-grade fever.  A sputum specimen was cultured for AFB and grew an organism at 14 days from Lowenstein-Jensen (LJ) medium incubated at both 42*C and 35*C. (8% CO2). The colony appeared “egg nest” like on the LJ medium.  The organism is identified as:

a.  Mycobacterium szulgai
b.  Mycobacterium chelonae
c.  Mycobacterium avium-intracellulare complex
d.  Mycobacterium xenopi
e.  Mycobacterium kansasii

8.  A 45 year old male with chronic lymphocytic leukemia develops painful nodular lesions on his chest. A biopsy of the nodules were submitted for AFB culture.  There was no growth on Lowenstein-Jensen medium at 37*C or 30*C (8% CO2).  The biopsy material grew when plated on a chocolate agar medium and incubated at 30*C (8% Co2)   The organism is most likely:

a.  Mycobacterium chelonae complex
b.  Mycobacterium fortuitum
c.  Mycobacerium abscessus
d.  Mycobacerium hemophilum
e.  Mycobacterium szulgai

9.  A 70 year old male developed numbness of the left earlobe.  A biopsy of the earlobe was submitted for AFB culture and submitted to anatomic pathology for staining.  The AFB culture showed no growth after 8 weeks when cultured on appropriate media at both 37* and 30 *C (8% Co2).  The Kinyoun/ZN type stain from tissue showed numerous AFB in a “school of fish” arrangement.  What statement(s) is not true:

a.  Mycobacterium leprae is the likely cause of this infection
b.  Real time PCR on the biopsy tissue could help establish the diagnosis
c.  Addition of hemin to the culture medium with help the organism grow
d.  The animal reservoir for this organism is the armadillo
e.  All of the above

10.  A 10 year old female developed a draining cervical lymph node.  The lymph node was biopsied and an AFB culture was submitted.  An AFB grew after 14 days on Lowenstein-Jensen medium at 37*C (8% CO2).  The colony was described as buff in color and cauliflower morphology.  Biochemical reactions include Niacin positive and Nitrate positive.  This infection is caused by:

a.  Mycobacterium scrofulaceum
b.  Mycobacterium tuberculosis
c.  Mycobacterium abscessus
d.  Mycobacterium chelonae complex
e.  Mycobacterium avium-intraceullare complex


1.  C
2.  D
3.  E
4.  B
5.  D
6.  B
7.  D
8.  D
9.  C
10. B

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