Bacteria separation from diluted blood
Before testing the behavior of bacteria spiked in blood, we tested how
bacteria behave in viscoelastic fluids. To demonstrate this, PEO was
spiked with fluorescently labelled gram negative Escherichia coli(E.coli ) and gram positive Staphylococcus capitis (Staph)(107 CFU/mL) processed through the spiral device at a
total flow rate of 1 mL/min in separate experiments. We observed a
similar behavior for both gram negative and gram positive with an yield
of 94% and 89% for E.coli and Staph respectively using
agar plating based quantification (supplementary Fig.S1). Following, to
study the separation of blood cells, lower concentration ofE.coli (103 CFU/mL) was spiked into 1:10, 1:5,
and 1:2 diluted blood. As expected, the bacteria migrated to the inner
wall and were collected at outlet O1, whereas blood cells stay near the
outer wall and collected at outlet O2 (Fig.5A). Quantification performed
using blood agar plating showed a separation efficiency of 82 to 90% ofE.coli (Fig.5B) depending on the dilution, while all blood cells
were recovered through the outer outlet for all cases. The higher blood
dilution, the higher bacteria separation efficiency, in agreement with
the results obtained for 1 µm particles (see Fig.4). While high
throughput is desirable for any application, need to process large
volumes is extremely very important for sepsis applications. Ideally,
this should not be on the cost of efficiency. Using our current spiral
device, considering only the sample flow rate of 50 µL/min, it takes 40
minutes to process 1 mL of whole blood at a separation efficiency of
82%. To the best of our knowledge, this is the highest efficiency yet
reported for a single device at an efficiency >80% using
passive separation methods. On the other hand, for a separation
efficiency of 90%, it would take approximately 3 hr to process 1 mL
blood.