Rogosa agar is an agar-containing solid medium, specifically used to grow lactobacilli in laboratory setups. It selectively allows the growth of most lactobacilli while inhibiting the growth of other bacteria (therefore called selective medium for Lactobacilli). Its ingredients include Tryptone, Yeast extract, Glucose, Potassium dihydrogen phosphate, Polysorbate 80 or Tween 80, Sodium acetate, Ammonium citrate, Magnesium sulphate, Manganese (II) sulphate, Iron (II) sulphate and Agar. It has a pH of 5.2 (adjusted using glacial acetic acid).
Tryptone and yeast extract are the source of nitrogenous compounds while vitamin B complex, and trace elements, and are essential for the growth of Lactobacilli. Glucose and Polysorbate 80 are the sources of carbohydrates and fatty acids respectively. The low pH of the Rogosa agar inhibits the growth of other bacteria while allowing Lactobacilli to grow. Ammonium citrate and sodium acetate are added to stop the growth of Streptococci and moulds.