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Principle
- Eosine Methylene Blue Broth is composed of peptone, lactose, sucrose, dipotassium phosphate, Eosin, and methylene blue. Peptone is a source of carbon, nitrogen, vitamins, and minerals.
- Lactose and sucrose are fermentable carbohydrates. Dipotassium phosphate acts as a buffer. Eosin and methylene blue are dyes that provide selectivity to media and act as pH indicators and inhibitors.
- The media is also used for the cultivation of 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 a change of pH, which solubilizes the methylene blue-eosin complex resulting, the color of media changes from light purple to pink or colorless.
- While the coliforms or lactose fermenters produce acid and decrease pH and media color changes from purple to dark purple with a greenish sheen, such as Escherichia coli forms characteristic green-colored metallic sheen. Gram-positive bacteria are partially inhibited on the medium.
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