Eosin-Methylene Blue Agar，EMB

Weak selective medium is used for isolation of enteric pathogens especially E. coli. Principle: EMB medium is commonly used for isolation and identification of E. coli and Enterobacteriaceae. Peptone provides carbon and nitrogen source; Lactose is fermentable sugar for coliforms; Potassium dihydrogen phosphate acts as a buffer; agar is gelling agent of the medium; Eosin is an acidic dye and methylene is an alkaline dye，both of which serve as indicator. When E. coli decomposes lactose to produce acid, it is positively charged and stained red, followed by binding with methylene blue to form purple-black colonies with a metallic sheen. Gas-producing Enterobacter species appear brown with little metallic sheen. Bacteria that do not compose lactose, such as Salmonella and Shigella, produce colorless or amber translucent colonies. Coagulase-positive Staphylococcus forms colorless pinhead-sized colonies. Candida albicans produces spiderweb-like or feathery colonies. Due to its weak inhibitory effect, this medium is not suitable for isolating enteric pathogens.