Evaluation of in vitro activities of tigecycline and various antibiotics against Brucella spp.

Brucellosis is a zoonosis with a worldwide distribution and remains a significant public health problem mainly in the developing world. In this study we evaluated the in vitro activities and synergistic effects of antibiotic combinations against blood culture isolates of Brucella spp. In vitro susceptibilities of 76 blood culture isolates of Brucella melitensis and one blood culture isolate of Brucella abortus to doxycycline, streptomycin, gentamicin, trimethoprim-sulfamethoxazole, moxifloxacin, rifampin, ciprofloxacin, and tigecycline were examined by Etest method. For 37 patients with Brucella spp. isolates (36 B. melitensis, 1 B. abortus), antibiotic combinations used for treatment were identified with those tested in vitro for synergy using Etest method. Trimethoprim-sulfamethoxazole and tigecycline were the most active of the compounds tested with MIC90 value of 0.094 mg/l. Among antibiotic combinations only streptomycin-rifampin combination was synergistic for one Brucella spp. isolate. The other antibiotic combinations revealed antagonistic or indifferent activity. Complete clinical response was achieved in all patients. Further studies are required to determine the correlation between the antimicrobial susceptibility and synergy test results with the clinical course of patients. Brucellosis can be adequately treated with existing regimens in our region.