In vitro activities of various antimicrobials against Brucella melitensis strains in the Aegean region in Turkey

Objective: To study in vitro activities of three quinolones (ciprofloxacin, levofloxacin, moxifloxacin), four macrolides (erythromycin, dirithromycin, azithromycin, clarithromycin) and doxycycline against 44 clinical isolates of Brucella melitensis.

Materials and methods: Forty-four B. melitensis strains were isolated from blood cultures of adult patients with acute brucellosis who were hospitalized in the clinical ward of the Department of Clinical Microbiology and Infectious Diseases. The minimum inhibitory concentrations (MICs) of the tested antimicrobials were measured by the agar dilution method. MIC90 and MIC50 values were defined as the lowest concentration of the antibiotic at which 90 and 50% of the isolates were inhibited, respectively.

Results: Doxycycline (MIC50: 0.25 microg/ml, MIC90: 0.50 microg/ml) had the lowest MIC in vitro against the B. melitensis strains. Among the quinolones, ciprofloxacin and levofloxacin had similar activities (MIC50: 0.5 microg/ml, MIC90: 2 microg/ml), whereas MIC of moxifloxacin (MIC50: 1 microg/ml, MIC90: 8 microg/ml) was higher than both antibiotics in this group. Clarithromycin and azithromycin were the most active macrolides (MIC50: 8 microg/ml and MIC90: 32 microg/ml), followed by erythromycin (MIC50: 16 microg/ml, MIC90: 32 microg/ml) and dirithromycin (MIC50: 64 microg/ml and MIC90: 64 microg/ml).

Conclusion: The results indicate that the conventional agent doxycycline is more active than quinolones and macrolides against the B. melitensis in vitro.