Antibiotic Medium No. 11

Antibiotic Medium No. 11

Official Seed Agar for Neomycin & Framycetin Cylinder-Plate Assays

Catalog Number: AS-1109

Overview

Antibiotic Medium No. 11 is the official standardized seed agar developed specifically for the microbiological cylinder-plate (cup-plate) assay of neomycin, framycetin, and related aminoglycoside antibiotics. It is designated as “Medium E” in USP <81>, European Pharmacopoeia 2.7.2, Japanese Pharmacopoeia (JP 17), and WHO guidelines.

The formulation is carefully adjusted to a slightly alkaline pH (7.9–8.1), which is essential for optimal aminoglycoside diffusion. When seeded with the appropriate test organism, this medium produces exceptionally sharp, large, and highly reproducible inhibition zones, making it the global reference medium for regulatory neomycin potency assays.

Key Features & Benefits

Slightly alkaline pH (≈ 8.0) optimised for neomycin diffusion

Internationally harmonised formulation (USP / EP / JP / WHO)

Produces the clearest and largest inhibition zones among neomycin assay media

High assay sensitivity and reproducibility

Official reference seed agar for regulatory testing

Typical Applications

Pharmaceutical Quality Control
Compendial potency assay of neomycin sulfate

Compendial potency assay of framycetin sulfate

Routine QC testing of aminoglycoside antibiotics

Cylinder-Plate Diffusion Assays
Assay of neomycin-containing ophthalmic products

Assay of topical and oral pharmaceutical formulations

Bioequivalence and batch-release testing

Principle of the Medium

Antibiotic Medium No. 11 provides an optimised nutrient base and alkaline environment that enhances aminoglycoside diffusion through agar. When inoculated with a sensitive test organism, neomycin and framycetin diffuse uniformly from cylinders or cups, producing inhibition zones whose diameter is directly proportional to antibiotic potency.

Typical Composition (per litre)

Peptone (meat or casein) – 6.0 g

Beef Extract – 1.5 g

Yeast Extract – 3.0 g

D-Glucose – 1.0 g

Agar – 15.0 g

Final pH: 7.9 – 8.1 at 25 °C (after sterilisation)

Preparation

Suspend 26.5 g of dehydrated medium in 1 L purified water

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

Sterilise by autoclaving at 121 °C for 15 minutes

After sterilisation, verify pH is 8.0 ± 0.1 (critical specification)

Cool to 48–50 °C

Inoculate with a standardised suspension of:

• Staphylococcus epidermidis ATCC 12228 (preferred), or

• Klebsiella pneumoniae ATCC 10031

Pour 4–6 mL of seeded medium over a previously prepared base layer
(typically Antibiotic Medium No. 2)

Storage & Stability

Dehydrated medium: Store below 30 °C in a cool, dry place

Prepared seeded plates: Use within 24 hours

If required, store at 2–8 °C for short periods only

Intended Use

For pharmaceutical quality-control and official compendial antibiotic assays only.
Not for clinical diagnostic, food, or veterinary use.

Quality & Compliance

Complies with USP <81>, EP 2.7.2, JP 17, and WHO requirements

Manufactured under controlled conditions for batch-to-batch consistency

Suitable for regulated pharmaceutical laboratories

Customs & Trade Information

HS / AHECC Code: 3821.00.00
Prepared culture media for development or maintenance of microorganisms