In vitro and in vivo susceptibility of the Lyme disease spirochete, Borrelia burgdorferi, to four antimicrobial agents.

The antimicrobial susceptibility of Borrelia burgdorferi isolated from human spinal fluid was determined in vitro and in vivo. A broth dilution technique was used to determine the MBCs of four antimicrobial agents. The Lyme disease spirochete was most susceptible to ceftriaxone (MBC, 0.04 microgram/ml) and erythromycin (MBC, 0.05 microgram/ml), then tetracycline (MBC, 0.8 microgram/ml), and finally penicillin G (MBC, 6.4 micrograms/ml). Syrian hamsters were used to determine the 50% curative doses (CD50s) of the four antimicrobial agents. Ceftriaxone and tetracycline had the highest activities, with CD50s of 24.0 and 28.7 mg/kg [corrected], respectively. Both erythromycin and penicillin G possessed low activities. The CD50 of erythromycin was 235.3 mg/kg [corrected], and the CD50 of penicillin G was greater than 197.5 mg/kg [corrected].