(134g) Sedimentation Separation of Red Blood Cells and Bacteria for Rapid Diagnosis of Blood Infections

Fast and efficient separation of bacteria from blood is the first step towards the rapid diagnosis of blood infections. We have developed a spinning hollow disk that separates blood cells from bacteria by capitalizing on the differences in sedimentation velocities of these particles. Hollow disks of various size and design were constructed to examine hypotheses relating to optimal collection of bacteria from blood and favorable separation of blood cells from the plasma. Disk design characteristics included the disk diameter, shape of the weir and trough, baffles, and fillets in corners. Blood processing characteristics included the spinning speed and duration, and the deceleration of the disk. Measured parameters were the volume of separated plasma, and the concentration of bacteria and red blood cells in the separated plasma. The data were correlated by a parameter of characteristic sedimentation length, which is the length that an idealized red blood cell would travel during the entire spin. The data from various disk sizes and spinning speed profiles were nicely correlated with this parameter. The results show that a characteristic sedimentation length of 20 to 25 mm produces an optimal collection of bacteria in plasma. This corresponds to spinning a 12-cm-diameter disk at 3,000 rpm for 13 seconds. Following the spin, a careful and slow deceleration preserves the separation of cells from plasma, and provides a bacterial recovery of around 60%. This is the first step in a diagnostic tool designed to identify bacteria in blood infections. Subsequent steps include lysing and recovery of bacterial DNA, hybridization of sequences identifying species and antibiotic resistance genes, fluorescent labeling, and optofluidic detection of the labeled DNA.