Speciation within the genus Brucella. III. Nitrate reduction and nitrite toxicity tests.

Reduction of nitrate has been employed by several workers as a test for distinguishing species in the genus Brucella (cf Huddleson, 1943). We examined this test briefly during our studies on the dye sensitivity of brucellae (Pickett et al., 1952) and concluded that it should serve at least as a useful guide for identification of the species. However, further study disclosed that the outcome of qualitative nitrate reduction tests is determined not only by the species but also by the nature and concentration of reductant in the test medium, the initial concentration of nitrate, the amount of inoculum, and the period of incubation. With these considerations in mind, we attempted to develop a nitrate reduction test which would serve as a useful adjunct for identification of these species. Though this attempt did not reach fruition, these studies did lead to the development of an alternative "nitrite toxicity" test which conveniently distinguishes Brucella melitensis.