Does bacterial contamination of platelet concentrates influence the leucocyte content and the rate of platelet storage lesion?

An observational study was carried out to assess the effect of bacterial gr owth on changes in platelet cellular indices and leucocyte content. Platele t derived from pooled buffy coats, with and without an additional leucocyte removal step by filtration and platelet derived from Cobe LRS system were used. These were spiked with two doses of several types of bacteria (1 and 50 CFU) in a paired control and test experiment. The changes in cellular pa rameters were monitored by an automated cell counter (Sysmex SE-9000) and t he concentration of the residual leucocyte were evaluated by two automated techniques, based on DNA staining principles (flow cytometry-EPICS-XL Coutt er and Imagn 2000). Our results indicate that initially bacterial growth is associated with a decrease in leucocyte count, followed by a concomitant i ncrease in platelet large cell ratio, possibly due to aggregate formation. During the prolonged storage a dramatic increase in pseudoleucocytes was ob served by both Imagn 2000 and flow cytometry techniques with an abnormal do t plot around FL3 regions in the latter counting method, making the true id entification of native leucocytes rather difficult. It is concluded that ba cterial growth is associated with both changes in platelet cellular indices and development of cellular aggregates and/or partially fragmented cells w ith DNA binding properties appearing as pseudoleucocytes. Further work on t he true nature of so called 'pseudoleucocyte' is in progress. (C) 2000 Else vier Science Ltd. All rights reserved.