Quality control is performed to test the validity of catalase production at 68°C. M. fortuitum and M. tuberculosis are used, which yield a positive and negative reaction, respectively. Which one of the following statements explains this discrepancy?
a. Both organisms were most likely incu-bated at the wrong temperature.
b. Both organisms were most likely incu-bated on the wrong media before testing.
c. The catalase reagent is most likely expired.
d. No discrepancy is present. M. fortuitum is catalase-positive and M. tuberculosis is catalase-negative at 68°C.
D
Because of the ability of the catalase enzyme to remain active after heating, a heat-stable catalase test that measures the heat stability of the enzyme is performed. When heated to 68°C for 20 minutes, the catalase of M. tuberculosis, M. bovis, Mycobacterium gastri, and M. haemophilum becomes inactivated. M. fortuitum remains positive.
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