Antibiotic Medium No. 8

Antibiotic Medium No. 8 (Streptomycin Seed Agar)

Official Seed Agar for Cylinder-Plate Antibiotic Assays
Catalog Number: AS-1119

Overview

Antibiotic Medium No. 8 is the official standardized seed agar used as an alternative to Antibiotic Medium No. 4 for the microbiological cylinder-plate assay of streptomycin and dihydrostreptomycin. It is designated as “Medium G” in USP <81>, European Pharmacopoeia 2.7.2, Japanese Pharmacopoeia (JP 17), and WHO guidelines.

The higher pH (8.0–8.2) and modified nutrient balance produce larger, sharper, and more reproducible inhibition zones with Bacillus subtilis ATCC 6633 compared to Medium No. 4 in many laboratories. As a result, Antibiotic Medium No. 8 is the preferred seed medium for streptomycin assays in current compendial protocols.

Applications

• Compendial seed layer for streptomycin and dihydrostreptomycin potency assays

• Cylinder-plate diffusion assays of streptomycin-containing pharmaceutical products

• Regulatory pharmaceutical quality-control testing
  (currently the most commonly accepted seed medium for streptomycin)

Key Features & Benefits

• Higher pH (8.1) maximizes streptomycin diffusion and inhibition zone size

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

• Produces exceptionally large, clear inhibition zones with Bacillus subtilis

• Reference seed agar in current streptomycin pharmacopeial monographs

Composition (per litre)

• Beef Extract – 1.5 g

• Yeast Extract – 6.0 g

• Peptone (meat or casein) – 6.0 g

• D-Glucose – 1.0 g

• Agar – 15.0 g

Final pH: 8.1 ± 0.1 at 25 °C (after sterilisation; strictly controlled)

Preparation

• Suspend 29.5 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

• Cool to 48–50 °C

• Inoculate with a standardized suspension of Bacillus subtilis ATCC 6633

• Pour 4–6 mL of seeded agar over a previously prepared base layer
  (typically Antibiotic Medium No. 5 or No. 2)

Test Organism (Mandatory)

• Bacillus subtilis ATCC 6633

Storage & Stability

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

• Prepared seeded plates: Use within 24 hours

• If required, store seeded plates at 2–8 °C for short periods

Note

In current editions of USP, European Pharmacopoeia, and JP, the combination of
Antibiotic Medium No. 8 + Bacillus subtilis has replaced Antibiotic Medium No. 4 + Klebsiella pneumoniae as the preferred system for streptomycin assays due to superior inhibition zone clarity and reproducibility.

Intended Use

For pharmaceutical quality-control and official compendial streptomycin assay applications only.
Not for clinical diagnostic, food, or veterinary use.

Quality & Compliance

• Official seed agar for streptomycin cylinder-plate assays

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

• Manufactured under controlled conditions for batch-to-batch consistency

• COA, SDS, and TDS available upon request

Customs & Trade Information

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