A and C to each culture. An orange color, which develops within 10 min, indicates that nitrate has been reduced to nitrite. Modified VP medium . Shake, and add a few crystals of creatine. Observe results after holding for 1 h at room temperature.
Test is positive if pink or violet color develops.
Tyrosine agar . Inoculate entire surface of tyrosine agar slant with 3 mm loopful of culture. Observe for clearing of medium near growth, which indicates that tyrosine has been decomposed. Examine negative slants for obvious signs of growth, and incubate for a total of 7 days before considering as negative. Lysozyme broth .