Tylosin (trade names Tylocine, Tylan) is a bacteriostat feed additive used in veterinary medicine. It has a broad spectrum of activity against Gram-positive organisms and a limited range of Gram-negative organisms. It is found naturally as a fermentation product of Streptomyces fradiae. It is a macrolide antibiotic. Tylosin is used in veterinary medicine to treat bacterial infections in a wide range of species and has a high margin of safety. Tylosin is certified by the FDA but is only approved for use in livestock such as cattle, chickens, swine, and turkeys. The FDA has prohibited the use of tylosin in dogs and cats, except where it is specifically prescribed by a veterinarian. Tylosin has a bacteriostatic effect on susceptible organisms, caused by inhibition of protein synthesis through binding to the 50S subunit of the bacterial ribosome.