Eosin-Methylene Blue Agar (EMB Agar)
Positive reaction: Escherichia coli.		Negative reaction: Klebsiella
This medium is used for differentation of Enterobacteriaceae. The medium contains sucrose and lactose. If the organism ferments sucrose and/or lactose, the pH in and around the colonies will fall below 5, causing the formation of a methylene blue eosinate complex which has a metallic sheen. At the same time, the colonies are dark in colour. Sucrose- and lactose-negative colonies are colourless or light purple in colour. The presence of eosin yellow and methylene blue in the medium inhibits Gram-positive bacteria.