In vitro susceptibilities of Rickettsia and Bartonella spp. to 14-hydroxy-clarithromycin as determined by immunofluorescent antibody analysis of infected Vero cell monolayers

The in vitro susceptibilities of Rickettsia akari, Rickettsia conorii, Rick ettsia prowazekii, Rickettsia rickettsii, Bartonella elizabethae, Bartonell a henselae and Bartonella quintana to different concentrations of clarithro mycin, 14-hydroxy-clarithromycin (the primary metabolite of clarithromycin) and tetracycline in Vero cell cultures, were determined by enumeration of immunofluorescently-stained bacilli. The extent of antibiotic-induced inhib ition of fool was recorded for each dilution of antibiotic and compared wit h an antibiotic-negative control. Based upon MIC data, clarithromycin alone is highly active against all three Bartonella spp., R. akari and R. prowaz ekii, while 14-hydroxy-clarithromycin is active against R, conorii, R. prow azekii and R. rickettsii. Further testing is warranted in animal models and human clinical trials, to examine the activity of both clarithromycin and its primary metabolite and to define further the role of clarithromycin in therapy, particularly of infections caused by obligate intracellular bacter ia such as Rickettsia and Bartonella spp.