TETRACYCLINE

any of a group of antibiotic compounds that have a common basic structure and are either isolated directly from several species of Streptomyces bacteria or produced semisynthetically from those isolated compounds. These drugs, which include chlortetracycline, oxytetracycline, tetracycline, demeclocycline, methacycline, doxycycline, and minocycline, are broad spectrum antibiotics, meaning they are effective against many different bacterial species as well as other types of microorganisms. They act by interfering with a microorganism's ability to produce certain vital proteins; thus they are inhibitors of growth (bacteriostatic) rather than killers of the infectious agent (bacteriocidal) and are only effective against multiplying microorganisms. These drugs are used against a variety of infectious diseases, including those caused by Rickettsia, Chlamydia, and Mycoplasma, as well as respiratory and urinary tract infections. By the late 20th century, concerns arose that the widespread use of tetracyclines was contributing to an increase in the number of tetracycline-resistant organisms, which in turn had rendered certain infections more resilient to treatment. The use of tetracyclines in livestock feed to promote growth was also called into question.