Susceptibility of Borrelia afzelii strains to antimicrobial agents.

The aim of the present study was to determine the susceptibility of Borrelia afzelii strains to antibiotics, and to test the hypothesis that persistence of borrelia in skin, after therapy, is a consequence of resistance to the antibiotic used for treatment. Ten B. afzelii strains isolated from skin of seven adult patients (two with acrodermatitis chronica atrophicans, five with erythema migrans) were studied. In three patients B. afzelii was isolated from erythema migrans lesion before antibiotic therapy and 2-3 months after treatment with cefuroxime axetil (two patients) or with ceftriaxone (one patient). MICs and MBCs for amoxicillin, azithromycin, ceftriaxone, cefuroxime, doxycycline and amikacin were measured. There was total resistance to amikacin but isolates were susceptible to all other antibiotics except one isolate that was resistant to cefuroxime, MIC > 4 mg/L. Comparison of MBC values after 3 and 6 weeks' incubation revealed comparable results for azithromycin and ceftriaxone while for amoxicillin, cefuroxime and doxycycline, some differences were found. In one of the patients from whom there were borrelia isolated before and after treatment with cefuroxime axetil, both isolates were resistant to cefuroxime. In the other two patients, the paired isolates were susceptible to the antibiotic used for therapy.