Antibiotic Medium Nº 3 is a standard medium prepared for use in antibiotic assays. The activity (potency) of an antibiotic can be demonstrated under suitable conditions by its inhibitoty effect on microorganisms. Reduction in antimicrobial activity may reveal changes not demonstrated by chemical methods. Antibiotic Medium Nº 3 can be used with the following microbiological methods for Antibiotic Assays: 1. Serial dilution method. 2. Turbidimetric method. Antibiotic Medium Nº 3 is used in the potency assay for penicillin, erythromycin, neomycin, chlortetracycline and chloramphenicol etc This medium can also be used in the turbidimetric determination. The turbidimetric method is based on the inhibition of growth of a microbial culture in a fluid medium containing a uniform solution of an antibiotic. Use of this method is appropriate only when test samples are clear. Peptone, yeast extract and beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Potassium phosphates act as a buffer system. Glucos is the fermentable carbohydrate providing carbon and energy. Bacteriological agar is the solidifying agent.
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