Antibiotics are drugs designed to treat bacterial infections such as urinary tract infections, strep throat, and tuberculosis. Antibiotics don’t treat viruses, like the flu or the common cold. They work by killing and/or stopping the multiplication of harmful bacteria that’s causing the illness. After only a couple days of antibiotic use, patients begin to feel better. Certain antibiotics are designed to kill a certain type of bacteria, while broad spectrum antibiotics are designed to kill a wide range of bacteria.