Comparison of in vitro activities of tigecycline, doxycycline, and tetracycline against the spirochete Borrelia burgdorferi

Tigecycline is a new glycylcycline that has recently been revealed to be very effective in vitro against a variety of Gram-negative and Gram-positive bacteria including multi-drug resistant microorganisms Using a standardized microdilution susceptibility testing method we determined the minimal inhibitory concentrations (MICs) and the minimal bactericidal concentrations (MBCs) of tigecycline in parallel with doxycycline tetracycline and other antibiotic agents relevant for Lyme borreliosis treatment such as ceftriaxone and cefotaxime The activity of all agents against 16 different Borrelia isolates belonging to all borrelial genospecies known to be pathogenic for humans was investigated and analyzed under standardized conditions The overall rank order of MIC(90)s was tigecychne (<= 0 016 mg/L) > ceftriaxone (0 03 mg/L) > cefotaxime ( 0 125 mg/L) > doxycycline (0 25 mg/L) > tetracycline (0 25 mg/L) The rank order of MBC(90)s was tigecycline (0 5 mg/L) > ceftriaxone (2 mg/L) > tetracycline (16 mg/L) > doxycycline (16 mg/L) > cefotaxime ( > 16 mg/L) High in vitro activity of the new glycylcycline against Borrelia was further substantiated by time-kill experiments performed with B afzelii isolate EB1 Parallel testing of tigecycline and ceftriaxone demonstrated a bacteriostatic effect for 0 016 mg/L of tigecychne and for 0 03 mg/L for ceftriaxone after 72 h of incubation Moreover tigecycline was bactericidal at a concentration of 025 mg/L showing a > 3 log(10) unit reduction of the initial inoculum whereas for ceftriaxone a concentration of 2 mg/L was needed (C) 2009 Elsevier GmbH All rights reserved