Each player begins with a card that represents one of four strains of bacteria. Each player maintains a hand of five cards that can include mutation cards that will permit the player to grow other players' strains in addition to his own. Other cards are random events, antibiotics (used to interfere with other players' cultures), and bacteria (used to help grow one's own cultures). Players play one or more cards on their turns, and play continues until all cards have been played. Players receive points based on the success of their cultures and a bouns if they have grown all four cultures.