Antibiotic Medium No. 12

Antibiotic Medium No. 12

Official Seed Agar for Nystatin & Polyene Antifungal Cylinder-Plate Assays

Catalog Number: AS-1112

Overview

Antibiotic Medium No. 12 is the official standardized seed agar used exclusively for the microbiological cylinder-plate (cup-plate) assay of nystatin and, where validated, other polyene antifungal antibiotics such as amphotericin B. It is designated as “Medium F” in USP <81>, European Pharmacopoeia 2.7.2, Japanese Pharmacopoeia (JP 17), and WHO guidelines.

The formulation features a slightly acidic pH (6.0–6.2) and enriched nutrient composition, optimised for rapid, uniform growth and maximum sensitivity of the required test organism. When properly prepared and seeded, the medium produces large, sharp, and highly reproducible inhibition zones, ensuring accurate potency determination for nystatin-containing pharmaceutical products.

Key Features & Benefits

Slightly acidic pH (≈ 6.1) critical for nystatin stability and zone formation

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

Produces clear, sharp, and highly reproducible inhibition zones

Official reference seed agar for nystatin assays

Validated for use with polyene antifungal antibiotics

Typical Applications

Official Compendial Assays
Potency assay of nystatin in oral suspensions, vaginal tablets, and topical powders

Cylinder-Plate Diffusion Assays
Assay of nystatin-containing pharmaceutical formulations

Assay of selected polyene antifungal products where validated

Pharmaceutical Quality Control
Regulatory batch-release testing

Stability and bioequivalence studies

Principle of the Medium

Antibiotic Medium No. 12 provides a nutritionally enriched agar base at a controlled acidic pH that supports uniform growth of the sensitive yeast test organism. Polyene antifungal antibiotics diffuse evenly from cylinders or cups, producing inhibition zones whose diameter is directly proportional to antifungal potency.

Typical Composition (per litre)

Peptone (meat or casein) – 6.0 g

Beef Extract – 1.5 g

Yeast Extract – 3.0 g

D-Glucose – 10.0 g

Agar – 15.0 g

Final pH: 6.1 ± 0.1 at 25 °C (after sterilisation)

Preparation

Suspend 35.5 g of dehydrated medium in 1 L purified water

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

Sterilise by autoclaving at 121 °C for 15 minutes

Cool to 48–50 °C

Inoculate with a standardised suspension of:

• Saccharomyces cerevisiae ATCC 9763 (preferred), or

• Candida albicans ATCC 10231 (as permitted by validated protocols)

Pour 4–6 mL of seeded medium over a previously prepared base layer
(typically Antibiotic Medium No. 1 or No. 2)

Required Test Organism

Saccharomyces cerevisiae ATCC 9763 (preferred)

Alternative (where pharmacopoeially validated):
Candida albicans ATCC 10231

Storage & Stability

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

Prepared seeded plates:
Use immediately, or
Store at 2–8 °C for a maximum of 24 hours

Critical Control Point

The final pH must be 6.1 ± 0.1.
Higher pH values significantly reduce inhibition zone size and assay accuracy.

Intended Use

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

Quality & Compliance

Formulated to meet USP <81>, EP 2.7.2, JP 17, and WHO requirements

Manufactured under controlled conditions for batch-to-batch consistency

Suitable for regulated pharmaceutical microbiology laboratories

Customs & Trade Information

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