Antibiotic Medium Nº 12 is recommended for preparing test plates for the cylinder plate assay of the antifungal agents nystatin and anisomycin, using only Saccharomyces cerevisiae as the test organism. It is used for the assay of amphotericin B. Peptone and Beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is source of vitamins, particularly the B-group. Sodium chloride supplies essential electrolytes for transport and osmotic balance. Dextrose is the fermentable carbohydrate providing carbon and energy. Bacteriological Agar is the solidifying agent. The potency of an antibiotic can be demonstrated under appropriate conditions by its inhibitory effect on microorganisms. This method is based on the diffusion of an antibiotic solution from a cylinder placed on the surface of an inoculated agar medium. The diameter of an inhibition zone after incubation depends, in part, on the concentration or activity of the antibiotic.
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