Comparison of different PCR methods for detection of Brucella spp. in human blood samples.

For detection of Brucella species by PCR four DNA extraction methods and four targets were compared using pure culture of Brucella melitensis and the best conditions were applied in clinical samples. It was found that the MagNA Pure LC method was the most efficient and sensitive method showing a positive PCR reaction with DNA extracted from as low as 25 and 100 CFU suspended in one ml blood and one ml water, respectively. Detection of Brucella spp. by conventional PCR was investigated using four different targets. The results indicated that The B4-B5 amplification method was the most sensitive one as it could amplify DNA extracted from as a low as 25 and 100 CFU/ml suspended in one ml water and blood, respectively. Furthermore real-time PCR was able to detect Brucella using DNA extracted from as low as 50 CFU/ml blood and 15 CFU/ml water, respectively. The best and optimum detection conditions were applied to the clinical samples. Evaluation of conventional PCR assays on blood specimens confirmed 72% of the results obtained by conventional blood culture methods with a specificity of 95%, while serum samples had a sensitivity of 54% and specificity of 100%. Real-time PCR was generally found to be more sensitive and specific for detecting Brucella spp. in blood and serum samples compared to conventional PCR. The real-time PCR done on blood specimens confirmed 77.5% of the results obtained by conventional blood culture methods with specificity of 100%, while 60% of serum samples were found to be positive with specificity of 100%. These results suggest that serum and blood analysis by conventional and real time PCR is a convenient and safe method for rapid and accurate diagnosis of brucellosis.