Antimicrobial susceptibility of Ehrlichia phagocytophila

Human granulocytic ehrlichiosis is a recently described disease caused by an obligate intracellular gramnegative organism recently named Ehrlichia phagocytophila, To expand our knowledge of the susceptibility of E. phagocytophila, we tested six New York State isolates for susceptibility to 12 antimicrobials using an HL-60 cell culture system. All of the isolates were susceptible to doxycycline (MIC, less than or equal to0.125 mug/ml; minimum bactericidal concentration [MBC], 0.125 to 0.5 mug/ml), rifampin (MIC, less than or equal to0.125 mug/ml; MBC, less than or equal to0.125 mug/ml), ofloxacin (MIC, less than or equal to2 mug/ml; MBC, less than or equal to2 mug/ml), levofloxacin (MIC, less than or equal to1 mug/ml; MBC, less than or equal to1 mug/ml), and trovafloxacin (MIC, less than or equal to0.032 mug/ml; MBC, less than or equal to0.032 mug/ml), Isolates were uniformly resistant to amoxicillin, ceftriaxone, erythromycin, azithromycin, clarithromycin, and amikacin, For one strain, the MBC of chloramphenicol was less than or equal to8 mug/ml. These data suggest that quinolone antibiotics and rifampin may be alternative agents for patients with intolerance to tetracyclines.