J Vet Sci. 2006 Dec;7(4):355-359   

In vitro susceptibilities of Leptospira spp. and Borrelia burgdorferi isolates to amoxicillin, tilmicosin, and enrofloxacin

Doo Kim1,2, Dorsey Kordick3, Thomas Divers1, Yung-Fu Chang1,*


1College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA. yc42@cornell.edu
2Department of Veterinary Medicine, Kangwon National University, Chunchon 200-701, Korea
3IDEXX Laboratories, Greensboro, NC 27410, USA


Antimicrobial susceptibility testing was conducted with 6 different spirochetal strains (4 strains of Leptospira spp. and 2 strains of Borrelia burgdorferi) against 3 antimicrobial agents, commonly used in equine and bovine practice. The ranges of MIC and MBC of amoxicillin against Leptospira spp. were 0.05-6.25 レg/ml and 6.25-25.0 レg/ml, respectively. And the ranges of minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of amoxicillin against B. burgdorferi were 0.05-0.39 レg/ml and 0.20-0.78 レg/ml, respectively. The ranges of MIC and MBC of enrofloxacin against Leptospira spp. were 0.05- 0.39 レg/ml and 0.05-0.39 レg/ml, respectively. Two strains of B. burgdorferi were resistant to enrofloxacin at the highest concentration tested for MBC (|100 レg/ml). Therefore, the potential role of tilmicosin in the treatment of leptospirosis and borreliosis should be further evaluated in animal models to understand whether the in vivo studies will confirm in vitro results. All spirochetal isolates were inhibited (MIC) and were killed (MBC) by tilmicosin at concentrations below the limit of testing (‖0.01 レg/ml).