Common antibiotics are medications used to treat bacterial infections. Penicillin (10 letters) is a type of antibiotic derived from a mold that was discovered in 1928 by Alexander Fleming. Neomycin (8 letters) is an antibiotic derived from bacteria and is used to treat a variety of infections. Erythromycin (12 letters) is a type of macrolide antibiotic and is used to treat a wide range of bacterial infections.