Antibiotic Assay Medium No. 19 is used for the microbiological assay of the antifungal agents Amphotericin B, Candicidin and Nystatin, with Saccharomyces cerevisiae as the test organism. Peptone, yeast extract, HM peptone, dextrose and sodium chloride in a firm agar base, final pH 6.1, give uniform lawns and clearly defined zones of inhibition for accurate potency determination by the agar diffusion method. A reference medium for pharmaceutical antibiotic assay laboratories. Dehydrated powder, store in a cool dry place. Packaged as 500 g.