In vitro susceptibility of Borrelia burgdorferi to 11 antimicrobial agents.

The in vitro susceptibility of Borrelia burgdorferi to 11 antimicrobial agents was investigated. The antimicrobial agents evaluated included ceftizoxime, FK037, cefotaxime, dirithromycin, clarithromycin and its metabolite 14-hydroxy-clarithromycin, erythromycin, doxycycline, amoxicillin, ciprofloxacin, and ofloxacin. Isolates of B. burgdorferi tested included two reference strains (B31 and ATCC 53899), six isolates from the midwestern United States, and three from Europe. A broth macrodilution method was used to determine MICs and MBCs. B. burgdorferi was inhibited by < or = 0.5 micrograms of each of the agents except the quinolones per ml. The MBCs for 90% of strains tested of ceftizoxime, FK037, clarithromycin, 14-OH clarithromycin, and dirithromycin (< or = 1.0 microgram of each per ml) were superior to those of amoxicillin (2.0 micrograms/ml) and doxycycline (4.0 micrograms/ml). Further in vivo studies are warranted to determine whether these agents may be efficacious in the treatment of Lyme borreliosis.