Antibiotics are medicines that fight bacterial infections in people and animals. They work by killing the bacteria or by making it hard for the bacteria to grow and multiply. Penicillins are a group of antibacterial drugs that attack a wide range of bacteria. They were the first drugs of this type that doctors used. In 1928, Alexander Fleming identified penicillin. Although Fleming technically discovered the first antibiotic, scientists had to do a lot of work before penicillins could become available for general use.