Antibiotic Medium No. 2

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, and 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, particularly 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 / ISO)

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 base medium for slow-diffusing antibiotics

Typical Applications

Base layer in cylinder-plate (cup-plate) antibiotic potency assays

Assay of aminoglycosides (gentamicin, streptomycin, kanamycin)

Assay of macrolides, lincosamides, tetracyclines, and chloramphenicol

Pharmaceutical quality-control 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.

Typical 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 of dehydrated medium in 1 L purified water

Heat with frequent agitation and boil for 1–2 minutes until fully dissolved

Sterilize by autoclaving at 121 °C for 15 minutes

Cool to 60–65 °C

Pour 20–25 mL into sterile 90–100 mm Petri dishes to form a uniform base layer (≈ 5–6 mm)

Allow to solidify on a level surface

Standard Usage

After solidification of the base layer, 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 desiccation

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