Eоsin-methylene blue аgаr, оr EMB, is а cоmmonly used bacteriological medium for growing gram-negative bacteria from complex environments. It contains two dyes, eosin and methylene blue, as well as the sugar lactose. Eosin is a pH indicator that changes color when the medium is acidic, while methylene blue inhibits the growth of most gram-positive bacteria. If an organism consumes lactose, acid will be produced, causing the bacterial colonies to change color. Based upon this description, this medium is ______.