Antimicrobial Susceptibility of Ehrlichia phagocytophila

Abstract

Human granulocytic ehrlichiosis is a recently described disease caused by an obligate intracellular gram-negative 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, ≤0.125 μg/ml; minimum bactericidal concentration [MBC], 0.125 to 0.5 μg/ml), rifampin (MIC, ≤0.125 μg/ml; MBC, ≤0.125 μg/ml), ofloxacin (MIC, ≤2 μg/ml; MBC, ≤2 μg/ml), levofloxacin (MIC, ≤1 μg/ml; MBC, ≤1 μg/ml), and trovafloxacin (MIC, ≤0.032 μg/ml; MBC, ≤0.032 μg/ml). Isolates were uniformly resistant to amoxicillin, ceftriaxone, erythromycin, azithromycin, clarithromycin, and amikacin. For one strain, the MBC of chloramphenicol was ≤8 μg/ml. These data suggest that quinolone antibiotics and rifampin may be alternative agents for patients with intolerance to tetracyclines.