Halim KAYSADU, YÜCEL DUMAN, YUSUF YAKUPOĞULLARI

nvestigation of Synergistic, Additive and Antagonist Effect of Antimicrobial Combinations Used for Brucella spp, with E-test Combination Method

Brucella spp. is a significant cause of morbidity and mortality in human. Though combination therapy is recommended in the patients with brucellosis, there is very less data about the in vitro efficacy of the combined antimicrobials. In this study, we aimed to investigate the in vitro activities of antimicrobial combinations used against the Brucella spp. strains. A total 40 human isolates of Brucella spp. strains were included in this study. In vitro activities of doxycycline, rifampin, cotrimoxazole, streptomycin and ciprofloxacin were studied by E-test (Bio Mérieux, France) strips. In vitro effectiveness of doxycycline-rifampin, rifampin-cotrimoxazole, doxycycline-streptomycin, ciprofloxacin-cotrimoxazole, and ciprofloxacin-streptomycin were investigated by E-test combination method, and the results were evaluated with Fractional Inhibitor Concentration Index. Cotrimoxazole was found as the most active antimicrobial against to tested Brucella isolates with the lowest Minimal Inhibitory Concentration (MIC) (as, 0.016 µg/ml), while rifampin was the least active drug with highest MIC (as 1.5 µg/ml). The MIC50 and MIC90 values of the tested antibiotics were as follows: cotrimoxazole 0.032 μg/ml and 0.064 μg/ml, doxycycline 0.064 μg/ml and 0.094 μg/ml, ciprofloxacin 0.094 μg/ml and 0.75 μg/ml, streptomycin 0.25 μg/ml and 0.50 μg/ml, and rifampin 0.50 μg/ml and 0.75 μg/ml, respectively. Doxycycline-rifampin combination showed a remarkable synergistic activity to all tested strains (%100), but rifampin-cotrimoxazole combination exhibited antagonist activity to two strains (5%). The ratios of synergistic activities were as follows: ciprofloxacin-streptomycine 57.5%, rifampin-cotrimoxazole 52.5%, doxycycline-streptomycin 32.5%, and ciprofloxacin-cotrimoxazole 25%. In this study, though cotrimoxazole was the highest in vitro active against to tested strains, its combination showed low synergistic effect with other antimicrobials. On the contrary, though rifampin showed low in vitro activity alone, it exhibited excellent synergistic effect when combined with doxycycline. Therefore, when the treatment is planned for a patient with Brucellosis, it will be benefit for testing the combination effectiveness of the drugs irrespective of their in vitro activities alone.

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