An improved reagent for mycobacterial nitrate reductase tests.

A new crystalline reagent for nitrate reductase tests was compared with standard liquid reagents on 437 strains of mycobacteria. The results for isolates of Mycobacterium avium complex, Mycobacterium kansasii, Mycobacterium gordonae, Mycobacterium scrofulaceum, Mycobacterium fortuitum, and Mycobacterium chelonei agreed 100% with the expected results. Of the 177 Mycobacterium tuberculosis isolates, 4 were negative by the conventional method. Two of these four isolates were positive with the new reagent. Of the positive nitrate tests carried out with liquid reagents, 42% flashed instantly or faded in color; none of the tests carried out with the new crystalline reagent flashed or faded. A stronger color reaction was seen for 28% of the positive tests with the new reagent.