Eosin-Methylene Blue Agar（EMB）（Granular）

Testing principle:Peptone serves as a basal nutrient source， providing nitrogen and other essential nutrients required for bacterial growth；Lactose serves as a fermentable carbon source; Eosin is an acidic dye， while Methylene Blue is a basic dye. When bacteria ferment lactose to produce acid， they carry a positive charge and bind with the negatively charged acidic dye Eosin， thereby taking on its color. Conversely， when bacteria produce abundant alkaline substances and carry a negative charge， they bind with the positively charged basic dye Methylene Blue， resulting in blue colonies. When bacteria produce large quantities of acid， the dyes precipitate as crystals， forming a metallic sheen. Dipotassium Hydrogen Phosphate maintains the buffering system; Agar serves as the solidifying agent.