Eosin Methylene Blue Agar

Principle

• Eosin methylene blue agar is composed of peptone, lactose, sucrose, dipotassium phosphate, Eosin Y, methylene blue, and agar.
• Peptone is a source of carbon, nitrogen, vitamins, and minerals. Lactose and sucrose are fermentable carbohydrates. Dipotassium phosphate act as a buffer.
• Eosin and methylene blue are dyes that provide selectivity to media and act as pH indicators and inhibitors.
• The media also differentiate between the lactose fermenters and non-lactose fermenters. Some gram-negative bacteria can not able to metabolize lactose or metabolize lactose very slowly. Hence, sucrose is used as the secondary carbohydrate source.
• While the lactose non-fermenters such as Salmonella sp. raise the pH of the surrounding by deamination of protein thus resulting in the change of pH, solubilizing the Eosin Methyl red complex, and growing as colorless colonies.
• While the coliforms or lactose fermenters produce acid and decrease pH abound the colonies, resulting in precipitation of both the dyes at acidic pH. produce black-purple colonies, such as Escherichia coli forms characteristic green-colored metallic sheen. Gram-positive bacteria are partially inhibited on the medium. Agar is a solidifying agent.

 Use:

Recommended for the differential isolation of the gram-negative Enteric Bacilli from clinical and nonclinical samples.