ANTIBIOTIC SUSCEPTIBILITY OF THE NEWLY CULTIVATED AGENT OF HUMAN GRANULOCYTIC EHRLICHIOSIS - PROMISING ACTIVITY OF QUINOLONES AND RIFAMYCINS

Human granulocytic ehrlichiosis (HGE) is a rapidly emerging tick-borne infection which presents as an acute febrile illness and is associate d with hematologic abnormalities, elevated hepatic transaminase levels , and characteristic intracellular organisms in peripheral blood granu locytes. Although HGE has been successfully treated with tetracyclines , its susceptibility to other antibiotics remains unknown, No clear tr eatment alternatives exist for young children, pregnant women, or alle rgic individuals, in whom tetracyclines are contraindicated, We perfor med in vitro antibiotic susceptibility tests with this recently isolat ed agent groan in the human promyelocytic leukemia cell line HL-60. Do xycycline (MIC, 0.25 mu g/ml), rifampin (MIC, 0.5 mu g/ml), rifabutin (MIC, less than or equal to 0.125 mu g/ml), ciprofloxacin and ofloxaci n (both with MICs of 2 mu g/ml), and trovafloxacin (MIG, less than or equal to 0.125 mu g/ml) demonstrated significant activity against the HGE agent, These agents were also bactericidal, The HGE agent was resi stant to clindamycin, trimethoprim-sulfamethoxazole, and imipenem-cila statin, as well as to ampicillin, ceftriaxone, erythromycin, and azith romycin, antibiotics commonly used to tl eat Lyme disease, Both chlora mphenicol and gentamicin had weak inhibitory activities hut were not b actericidal. Our findings confirm the observed clinical efficacy of do xycycline and further suggest that the rifamycins and quinolones, part icularly trovafloxacin, hold promise as alternative agents for treatin g this new infection.