Overview:
Antibiotic Medium No. 11 is the official standardized seed agar specifically developed for the microbiological cylinder-plate assay of neomycin, framycetin, and related aminoglycoside antibiotics. It is designated as �Medium E� in USP <81>, European Pharmacopoeia 2.7.2, JP 17, and WHO guidelines. The adjusted pH (7.9�8.1) and optimized nutrient composition produce extremely sharp, large, and reproducible inhibition zones with the test organism Klebsiella pneumoniae or Staphylococcus epidermidis.
Applications:
?? Compendial potency assay of neomycin sulfate and framycetin sulfate
?? Cylinder-plate diffusion assay for neomycin-containing pharmaceutical products (ophthalmic, topical, oral)
?? Quality-control testing in pharmaceutical laboratories
Key Features:
?? Slightly alkaline pH (8.0) � essential for maximum neomycin diffusion and zone clarity
?? Internationally harmonized formulation (USP/EP/BP/JP/WHO)
?? Produces the clearest and largest zones among all neomycin assay media
?? Reference medium for all regulatory neomycin assays
Composition (per liter):
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 sterilization; critical specification)
Preparation:
Suspend 26.5 g of the dehydrated medium in 1 liter of purified water. Heat with frequent agitation and boil for 1�2 minutes until completely dissolved. Sterilize by autoclaving at 121�C for 15 minutes. After sterilization, the pH must be 8.0 � 0.1. Cool to 48�50�C. Inoculate with standardized suspension of:
Staphylococcus epidermidis ATCC 12228 (preferred), or
Klebsiella pneumoniae ATCC 10031.
Pour seeded layer (4�6 mL) over a previously prepared base layer (usually Antibiotic Medium No. 2).
Storage:
Dehydrated medium: Store below 30�C in a cool, dry place.
Prepared seeded plates: Use within 24 hours; store at 2�8�C if necessary.
Note: The final pH of 8.0 is absolutely critical � lower pH dramatically reduces zone size and assay sensitivity.
For pharmaceutical quality-control and official compendial antibiotic assay only.