Any of a class of broad-spectrum antibiotic s with a common basic structure, including doxycycline.
They may be isolated directly from several species of actinomycete s of the genus cholera , rickettsial infections (see rickettsia ), psittacosis, brucellosis , and tularemia; tetracyclines are also used in the treatment of acne . Overuse of these and other antibiotics has led to drug resistance in microorganisms.