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In the same medium, weak fermenters form small amounts of acid, which are frequently masked by the alkaline products of the peptone. Oxidizers, as a rule, produce even less acid, which is, with few exceptions, neutralized. This is the very reason why the carbohydrate spectrum of oxidizers must not be examined in media rich in peptone. 5 (Andrade’s, bromocreso! purple). 0 (bromothymol blue, phenol red) are used. The carbohydrate spectrum of fermenters that have no special nutritional requirements (Enterobacteriaceae, Vibrionaceae, Staphylococcus) is usually tested in classical 1 YOpeptone water or broth containing the substrates and the indicator.

E. , 1963; Cowan, 1974; MacFaddin, 1980). Testing of nitrate decomposition is of great value in identification. Acinetohacter, Fluvobucterium, Alcaligenes odorans and some other aerobes and many anaerobic bacteria do not attack nitrate. Most bacteria, including Enterobacteriaceae produce nitrite, whereas Pseudomonas ueruginosa and some other pseudomonads and Alcaligenes denitrtficans produce nitrogen gas. Denitrification to substances other than nitrogen gas is not distinguished in practical diagnostic work from nitrogen-gas production.

In the case of anaerobes, pipette the culture from under the paraffin oil into an empty tube and add the xylene and Ehrlich’s reagent, as above. (iii) Interpretation. Positive: pinkish-red ring below the xylene layer (Flavobacterium meningosepticum and Propionihacterium acnes). Negative: no colour reaction (Flavohacterium odorutum and Peptostreptococcus anaerohius). The test medium should be prepared with peptones yielding, on utilization, a sufficient amount of tryptophan, and should not contain fermentable sugars.