MATERIALS AND METHODSDetection of microorganisms in blood samplesThe presence of microorganisms in blood samples of hospitalized patients was detected using the BacT/ALERT microbial detection system (bioMérieux, Marcyl'Etoile, France ). Samples were inoculated into standard aerobic and standard anaerobic BacT/ALERT blood culture bottles, which were transferred to the Bactec 9240 instrument (software version V4.70A) to monitor bacterial growth. Positive blood cultures containing Gram-negative rods and Gram-positive cocci that appeared monomicrobial on Gram staining were included in the study. In total, 233 consecutive positive aerobic blood cultures were analyzed, including 159 cultures with Gram-negative bacilli and 67 with Gram-positive cocci. Direct identification of bacteria using the VITEK 2 ID System Bacteria were directly identified using samples from blood culture bottles that were incubated for 4-24 hours at 35°C. From each vial, 3 ml or 9 ml of fluid was sampled (for Gram positive cocci) and first centrifuged at 150 g for 10 minutes in order to isolate blood cells (in the pellet). Bacterial cells were then harvested by centrifuging (at 1000 g for 10 min) a mixture of 2 ml of supernatant with 1 ml of 0.45% saline to eliminate residual red blood cells by lysis. A bacterial suspension was prepared by mixing the pellet with 0.45% saline to obtain a concentration of 0.5–0.63 McFarland units using the VITEK Densichek colorimeter (bioMérieux). When no bacterial sediment was observed after the second centrifugation for Gram-positive bacteria, 1.5 ml of 0.45% saline and 3 ml of Brain-Heart Infusion (BHI) were added and the tube was incubated under stirring at 37°C for 2 hours to induce better growth. Bacteria (2 ...... half of paper ......y bacteria that were correctly identified by the standard method were included in the comparison exercise. The results of the direct identification method were reported as correctly identified, incorrectly identified and not identified. VITEK 2 ID system, Klebsiella pneumoniae subsp. (planticola/terrigena) and K. pneumoniae subsp ozaenae were considered identical and reported as direct method K. category (complete agreement between the two methods), minor discrepancy (sensitive or resistant with the direct method and intermediate with the standard method or vice versa), major discrepancy (resistant with the direct method but sensitive with the standard method) and very important discrepancy (sensitive with the direct method but resistant with the standard method).