Novel flow cytometric screening method for bacterial contamination of red blood cells: a proof‐of‐principle evaluation

Abstract

Platelet concentrates (PCs) are the major source of transfusion-transmitted bacterial infection but the significantly higher number of transfused red blood cells (RBCs) has resulted in a similar occurrence of possible transfusion-associated bacterial infections as those of recipients transfused with platelets. The aim of this study was adaption of the BactiFlow (BF) flow cytometric rapid PC screening method for the detection of bacterial contamination in RBCs. The BF assay was used to detect and count bacteria based on esterase activity in viable cells in RBCs. The initial sample preparation for RBCs included the lysis of RBCs, followed by enrichment of bacteria by centrifugation and subsequent standard PC sample preparation. Two-hundred RBC units were analyzed by BF and the BacT/Alert automated culture system. Furthermore, RBCs were spiked with eight different bacteria to monitor bacterial growth kinetics. The BF showed an excellent correlation to conventional plate count results after RBC sample processing. The diagnostic sensitivity of the assay was determined to fewer than 500 counts/mL. Analysis of RBC units showed concordant negative results by BF and culture. Growth kinetics of bacteria were successfully monitored using flow cytometry, showing that Yersinia enterocolitica or Serratia liquefaciens had the capability to grow in RBCs to high counts. Our study demonstrates the successful modification and application of a rapid flow cytometric screening method for bacterial contamination in RBCs. The BF assay represents a powerful basic tool to study bacterial contamination, potential screening strategies of RBCs, and the clinical outcome of screened RBCs prepared for transfusion.