buffered charcoal yeast extract agar buffered charcoal yeast extract agar buffered charcoal yeast extract (bcye) agar is a selective growth medium used to culture or grow certain types of bacteria, particularly the gram-negative species legionella pneumophila. it has also been used for the laboratory diagnosis of acanthamoeba keratitis, francisella and nocardia. composition of bcye agar medium ingredientamount (g/l)purpose agar12.0solidifying yeast extract10.0vitamins, nitrogen, and carbon aces buffer10.0buffer activated charcoal2.0decomposes hydrogen peroxide, a toxic metabolite of legionella potassium hydroxide2.8ph (target shall be 6.9±0.2) alpha-ketoglutarate1.0stimulates oxygen-scavenging enzymes in legionella l-cysteine0.4 provide absolutely essential nutrients to legionella ferric pyrophosphate0.2 this culture is to be differentiated from regular yeast extract agar, which is not selective.