Comparison of E Test to Microdilution for Determining In Vitro Activities of Antibiotics against Brucella melitensis

The standard procedures for in vitro testing have not been determined for brucellae. We compared two susceptibility testing methods for this organism. Isolates were from blood or bone marrow cultures of patients admitted to Hacettepe University Hospital. MICs were determined by microdilution testing of 22 strains for the following antibiotics: azithromycin (Pfizer), doxycycline (FAKO), ofloxacin (Hoechst Marion Roussel), rifampin (Sigma), and streptomycin (Sigma). Antibiotics were diluted twofold in Mueller-Hinton broth (Oxoid), supplemented with 1% PoliViteX (BioMerieux). Bacterial inoculum was prepared by adjusting the turbidity of the 48-h broth culture to that of a 0.5 McFarland turbidity standard to give a final inoculum of 105 to 106 CFU/well. The microplate trays were incubated at 35°C in ambient air, and the results were read after 48 h. The lowest antibiotic concentration that completely inhibited visible growth was considered to be the MIC (4).