Antibiotic Medium No. 2 (Penassay Base Agar)
Base-Layer Agar for Cylinder‑Plate (Cup‑Plate) Antibiotic Assays
Catalog Number: AS‑1109
 
Overview
Antibiotic Medium No. 2 is the official standardized base‑layer agar used in the cylinder‑plate (cup‑plate) microbiological assay of antibiotics. Internationally designated as “Medium B”, it is specified in all major pharmacopoeial and regulatory standards, including:
USP <81>
European Pharmacopoeia 2.7.2
British Pharmacopoeia
Japanese Pharmacopoeia (JP 17)
FDA (21 CFR 436.102)
WHO
ISO 20776‑2
When used as a base layer and overlaid with a seeded assay layer (typically Antibiotic Medium No. 1 or No. 11), this medium produces large, sharp, and highly reproducible inhibition zones, especially for slow‑diffusing antibiotics or assays requiring a thicker agar foundation.
Ausamics Antibiotic Medium No. 2 is manufactured to deliver consistent diffusion performance, reliable zone definition, and full compendial compliance for pharmaceutical quality‑control laboratories.
 
Key Features & Benefits
Internationally harmonised formulation (USP / EP / BP / JP / WHO / FDA)
Designed specifically as the base layer in cylinder‑plate assays
Higher peptone and beef extract content for improved antibiotic diffusion
Slightly higher pH (6.9–7.0) than Medium No. 1 for enhanced zone clarity
Produces larger, clearer, and more reproducible inhibition zones
Gold‑standard medium for slow‑diffusing antibiotics
 
 
Typical Applications
Base layer in cylinder‑plate (cup‑plate) antibiotic potency assays
Assay of:
Aminoglycosides (gentamicin, streptomycin, kanamycin)
Macrolides
Lincosamides
Tetracyclines
Chloramphenicol and related antibiotics
Pharmaceutical QC testing
Reference medium for antibiotic content, potency, and bioequivalence studies
 
Principle of the Medium
Antibiotic Medium No. 2 provides a nutrient‑rich, firm agar base that supports uniform diffusion of antibiotics from cylinders or cups into the agar matrix. Its optimized nutrient balance and agar concentration ensure stable growth conditions in the overlaid seeded medium, enabling accurate zone measurement and high assay reproducibility.
 
Composition (per litre)
Beef Extract – 1.5 g
Yeast Extract – 3.0 g
Peptone (meat or casein) – 6.0 g
D‑Glucose – 1.0 g
Agar – 17.0 g Final pH: 6.9 ± 0.1 at 25 °C (after sterilization)
 
Preparation
Suspend 28.5 g dehydrated medium in 1 L purified water
Heat with frequent agitation and boil for 1–2 minutes until fully dissolved
Autoclave at 121 °C for 15 minutes
Cool to 60–65 °C
Pour 20–25 mL into 90–100 mm Petri dishes to form a uniform base layer (~5–6 mm)
Allow to solidify on a level surface
 
Standard Usage
After the base layer has solidified, overlay with 4–6 mL of seeded Antibiotic Medium No. 1 or No. 11 containing the appropriate test organism, following the relevant compendial method.
 
Storage & Stability
Dehydrated medium: Store below 30 °C in a cool, dry place
Prepared base‑layer plates: Store at 2–8 °C, protected from light and drying
Shelf life (prepared plates): Use within 7 days
 
Intended Use
For pharmaceutical quality‑control and compendial antibiotic assay applications only. Not for clinical diagnostic, food, or veterinary use.
 
Quality & Compliance
Meets USP, EP, BP, JP, FDA, WHO, and ISO requirements
Suitable for regulated pharmaceutical microbiology laboratories
Performance comparable to leading international reference media
 
Customs & Trade Information
HS / AHECC Code: 3821.00.00 Prepared culture media for development or maintenance of microorganisms
 
Why Buy Antibiotic Medium No. 2 from Ausamics?
Ausamics is an Australian life‑science supplier specialising in microbiological culture media for regulated laboratories, offering:
Compendial‑grade formulations
Consistent batch quality and documentation
Competitive alternatives to global brands
Reliable supply with international shipping