Susceptibility of the Relapsing-Fever Spirochete Borrelia miyamotoi to Antimicrobial Agents.

Hard-tick-borne relapsing fever (HTBRF) is an emerging infectious disease throughout the temperate zone caused by the relapsing-fever spirochete Antibiotic treatment of HTBRF is empirically based on the treatment of Lyme borreliosis; however, the antibiotic susceptibility of has not been studied to date. Thus, we set out to determine the antimicrobial susceptibility of A microdilution method with 96-well microtiter plates was used to determine the antibiotic susceptibilities of two strains isolated on two different continents (Asia and North America), two strains, and one isolate for purposes of comparison. The MIC and minimal bactericidal concentration (MBC) were determined by both microscopy and colorimetric assays. We were able to show that relative to the isolates, both strains and demonstrated greater susceptibility to doxycycline and azithromycin, equal susceptibility to ceftriaxone, and resistance to amoxicillin The MIC and MBC of amoxicillin for evaluated by microscopy were 16 to 32 mg/liter and 32 to 128 mg/liter, respectively. Since is susceptible to doxycycline, azithromycin, and ceftriaxone , our data suggest that these antibiotics can be used for the treatment of HTBRF. Oral amoxicillin is currently used as an alternative for the treatment of HTBRF; however, since we found that the strains tested were resistant to amoxicillin , this issue warrants further study.