Acetate Differential Agar is used to test the ability of an organism to use acetate as the sole source of carbon. Most bacteria can use citrate and acetate with organic nitrogen present. Simmons Citrate Agar was elaborated by Simmons to measure citrate use without the presence of organic nitrogen. Trabulsi and Ewing replaced sodium citrate with sodium acetate in their formulation of Acetate Differential Agar. The medium contains a mixture of salts and Sodium acetate, as a sole source of carbon, which results in the production of alkaline products. The increment in pH creates a blue color in the medium due to the presence of Bromothymol blue. Dipotassium phosphates act as a buffer system.Bacteriological agar is the solidifying agent. Typical cultures of Shigella are unable to use acetate and fail to grow; therefore, the medium remains unchanged. The majority of Escherichia coli grow well within 24-48 hours, but some strains grow more slowly and may give a false-negative reaction if results are observed at 24-48 hours only. The growth is indicative of the use of Acetate.
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