Indications for Tetracyclines Tetracyclines are active against infections caused by the following: Rickettsiae Spirochetes (eg, Treponema pallidum, Borrelia burgdorferi) Helicobacter pylori Vibrio species Yersinia pestis Francisella tularensis Brucella species Bacillus anthracis Plasmodium vivax Plasmodium falciparum Mycoplasma species Chlamydia and Chlamydophila species Some methicillin-resistant Staphylococcus aureus About 5 to 10% of pneumococcal strains and many group A beta-hemolytic streptococci, many gram-negative bacillary uropathogens, and penicillinase-producing gonococci are resistant.