Eosin Methylene Blue Agar (EMB Agar)
Eosin Methylene Blue Agar (EMB Agar) is a widely used selective and differential medium for the isolation of Gram-negative enteric bacteria, particularly coliform and fecal coliform groups. It differentiates lactose fermenters and non-fermenters based on colony morphology and color changes.
Formula Composition
| Ingredient |
Function |
| Peptone |
Supplies carbon and nitrogen sources for bacterial growth |
| Lactose |
Fermentable carbohydrate for coliform bacteria |
| Dipotassium hydrogen phosphate |
Buffering agent to stabilize pH |
| Agar |
Gelling agent |
| Eosin & Methylene Blue |
Selective inhibitors against Gram-positive bacteria, pH indicators |
Test Principle
Peptone provides carbon and nitrogen sources to support bacterial growth. Lactose acts as fermentable sugar for the Escherichia coli group. Dipotassium hydrogen phosphate functions as a buffer. Agar serves as the gelling agent. Eosin and methylene blue work as both antibacterial agents and pH indicators. They inhibit Gram-positive bacteria and form precipitates under acidic conditions. Lactose-fermenting strains develop purple-black colonies or colonies with black centers and colorless transparent peripheries.
Directions for Use
Take one sachet of the product, add it into 200 mL distilled or deionized water, stir and heat to boiling until fully dissolved. Autoclave at 121 ℃ for 15 minutes. Cool the medium to approximately 50 ℃, pour into sterile plates under aseptic conditions, allow it to solidify, and reserve for use.
