Schematic representation of the two states of the system. State 1: Low survival rates: If the expression of aphII is low, AphII is not abundant and most ribosomes are poisoned. This poisoning leads to a further reduction of AphII abundance and thus to low survival rates. State 2: High survival rates: If the expression of aphII is high, AphII is abundant, more neomycin is inactivated so less ribosomes are poisoned and high survival rates are observed. A small variation of aphII expression around a specific threshold leads to an abrupt switch from one state to the other.