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Background & Objective: Brucellosis is one of the most common zoonotic diseases in Iran and is endemic in all parts of the country. Patients recorded in 1988 were 71,051(132. 4 per 100,000). Brucella species are facultative intracellular bacteria, and therefore a limited number of antibiotics are effective against these organisms. The aim of this study was the
evaluation of in vitro sensitivity of various antimicrobial agents against 47 brucella melitensis strains isolated from blood culture.
Methods: The susceptibility of 47 Brucella melitensis isolates derived from clinical samples were tested in vitro. 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 percent of the isolates
were inhibited, respectively. The NCCLS criteria for slow growing bacteria were considered to interpret the results.
Results: Tetracycline (MIC50: 0.13μg/ml, MIC90: 0.25 μg/ml) and streptomycin (MIC50:0.003 μg/ml, MIC90:0.25 μg/ml) had the lowest MICs in vitro against the B. melitensis strains. Norfloxacin had the highest (8 μg/ml) MIC90 value. More than half
isolates presented reduced susceptibility to rifampin (MIC value: 2μg/ml).
Conclusion: Brucella isolates remain susceptible in vitro to most antibiotics used for treatment of brucellosis. There is no significantly important resistance problem for antibiotics targeted against Brucella species in Iran. However, since rifampin is commonly used for prevalent diseases such as tuberculosis, the regional susceptibility pattern of rifampin should be assessed periodically.