Antibiotic Medium No. 1 — Official Standardized Assay Medium CAT: AS‑1108
Overview
Antibiotic Medium No. 1 (CAT: AS‑1108) is the globally recognized solid medium used for antibiotic potency assays by the cylinder‑plate (cup‑plate) and turbidimetric methods. Originally formulated by Grove and Randall (1955), it is specified as “Medium A” in FDA (21 CFR 436.102), USP <81>, EP 2.7.2, JP 17, WHO, and ISO 20776‑2 standards.
This medium provides optimal growth conditions for inoculum organisms such as Staphylococcus aureus, Bacillus subtilis, Kocuria rhizophila, and Bordetella bronchiseptica, ensuring sharp, reproducible inhibition zones for accurate potency determination.
 
Applications
Microbiological assay of antibiotics (penicillins, tetracyclines, aminoglycosides, macrolides, etc.).
Cylinder‑plate and agar‑diffusion potency testing.
Seed agar for turbidimetric antibiotic assays.
Quality‑control testing in pharmaceutical laboratories.
 
Key Features
Globally harmonized formulation (USP/EP/BP/JP/WHO/ISO).
Reproducible assay results with sharp zone edges.
Low variability between laboratories and batches.
Reference medium for regulatory antibiotic potency determination.
 
Composition (per liter)
Beef Extract: 1.5 g
Yeast Extract: 3.0 g
Peptone (meat or casein): 6.0 g
D‑Glucose: 1.0 g
Agar: 15.0 g
Final pH: 6.6 ± 0.1 at 25 °C (after sterilization)
 
Preparation
Suspend 26.5 g of dehydrated medium in 1 L purified water.
Heat with frequent agitation; boil for 1–2 minutes until dissolved.
Dispense as required.
Sterilize by autoclaving at 121 °C for 15 minutes.
Cool to 45–50 °C for pouring seed layers (1–2 mm base layer, 3–4 mm seed layer with inoculum).
 
Storage
Dehydrated medium: Store below 30 °C in a cool, dry place.
Prepared plates: Store at 2–8 °C, protected from light and desiccation.
Use within 7 days.
 
Standard Test Organisms
Staphylococcus aureus ATCC 6538P / NCTC 7447
Bacillus subtilis ATCC 6633
Kocuria rhizophila ATCC 9341
Bordetella bronchiseptica ATCC 4617
 
Safety & Compliance
For laboratory and pharmaceutical quality‑control use only.
Legally recognized as a standard medium for antibiotic assay.
COA, SDS, and TDS available upon request.