Antibiotic susceptibilities of 18 B. burgdorferi sensu lato isolates to β-lactams, macrolides, and doxycycline, as determined in BSKa

Isolated or parameterConcn (μg/ml) of antimicrobial agentb
B. spielmanii
B. burgdorferi sensu stricto
B. afzelii
B. garinii
All Borrelia isolates
    MIC or MBC range0.0625-0.52-320.0079-0.06251->40.001-0.01560.25-4≤0.125-42->16≤0.063-0.251->80.0156-0.1250.25-4
    MIC90 or MBC90c0.25160.031240.007912>160.25>80.06254
S. aureus ATCC 29213e
    Median MIC0.250.250.063224
    CLSI MIC range0.12-0.50.25-10.12-0.50.12-0.50.5-21-8
  • a Antimicrobial susceptibility was determined on three different days, and MICs and MBCs for each isolate are reported as the medians from three experiments.

  • b The test ranges (in μg/ml) were as follows: for doxycycline, 0.016 to 32; for erythromycin and clarithromycin, 0.0002 to 4; for amoxicillin, 0.125 to 16; for ceftriaxone, 0.004 to 8; and for cefuroxime, 0.063 to 8.

  • c MBC90, MBC required to kill 90% of the isolates.

  • d Geographic and clinical characteristics of the strains are as follows: isolates PMew, PSigII, PHap, PMai, PSth, LW2, and FEM1 were recovered from skin samples in Germany; isolate PC-Eq17 was recovered from a tick in France; isolates PAnz, PJes, G600, G1039, and M2094 were recovered from skin samples in Slovenia; isolate A14S was recovered from a skin sample in The Netherlands; isolates TIsar2 and TIsar3 were recovered from ticks in Germany; isolate G1 was recovered from cerebrospinal fluid in Germany; and isolate B31 was recovered from a tick in the United States.

  • e To investigate significant antibiotic-medium interaction, MICs for S. aureus (ATCC 29213) were determined on three different days, referring to the CLSI method (5), except for the use of BSK and preincubation of the antibiotic-medium test preparation for 48 h before testing. Results are reported as the medians from all three experiments.