tetracycline (tĕˌtrəsĪˈklēn) [key], any of a group of antibiotics produced by bacteria of the genus Streptomyces. They are effective against a wide range of Gram positive and Gram negative bacteria, interfering with protein synthesis in these microorganisms (see Gram's stain). Tetracycline is used to treat rickettsial bacterial infections such as Rocky Mountain spotted fever, some eye, respiratory, intestinal, and urinary infections, some kinds of acne, and some diseases where the infecting microorganism is resistant to penicillin (see drug resistance). Tetracycline may cause permanent discoloration of developing teeth, and it is not given to pregnant and lactating women and growing children. Because of the development of strains of microorganisms resistant to the tetracyclines, these antibiotics have lost some of their usefulness. Aureomycin is a trade name for the derivative chlortetracycline, and Terramycin is a trade name for oxytetracycline.