Antibiotic Medium N°1 EP/USP
Suspend 30.5 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121ºC for 15 minutes. The prepared medium should be stored at 8-15°C. The color is amber, slightly opalescent.
The dehydrated medium should be homogeneous, free-flowing and beige in color. If there are any physical changes, discard the medium.
ANTIBIOTIC MEDIUM Nº 1 is used for testing the potency of antibiotics through their inhibitory effects on microorganisms. The cylinder assay plate is based on the diffusions of the antibiotics under test, measuring the size of the inhibition zones of microorganisms.
Peptones, Yeast extract and Beef extract provide nitrogen, vitamins, minerals and amino acids essential for growth. Bacteriological Agar is the solidifying agent.
Seed Agar is used as an inoculum substrate. It is cooled to 48°C and inoculated accordingly with the specific antibiotics under test. Use 2 ml of the liquid culture to inoculate 100 ml of the Seed Agar. Agitate the mixture gently to produce ahomogeneous distribution and pour 4 ml on each plate of solidified Base Agar (21 ml).
It is very important that the seed layer is evenly distributed over the entire surface of the Base Agar. Once the seed layer is solid, the cylinders are placed evenly spaced on a 2.5 - 3 mm radius. The standard sample is added as described above. This method is used for testing the potency of bacitracin and penicillin preparations.
Seed Agar is used for the basic layer as well as the seed layer for the assay of chloramphenicol in plates. A medium with a higher pH and the same formula is used for the assay of erythromycin, carbomycin and neomycin: Neomycin Test Agar (Antibiotic Medium Nº 11, Cat. 1528