What type of bacteria are inhibited on MacConkey agar?

MacConkey agar is a selective and differential medium that inhibits the growth of gram-positive bacteria while allowing gram-negative bacteria to grow. It contains bile salts and crystal violet, which inhibit gram-positive organisms, and also differentiates bacteria based on their ability to ferment lactose (lactose-fermenters produce pink colonies, while non-lactose fermenters produce colorless colonies).