High-volume extraction of nucleic acids by magnetic bead technology for ultrasensitive detection of bacteria in blood components

Abstract

Background: Nucleic acid isolation, the most technically demanding and laborious procedure performed in molecular diagnostics, harbors the potential for improvements in automation. A recent development is the use of magnetic beads covered with nucleic acid-binding matrices. We adapted this technology with a broad-range 23S rRNA real-time reverse transcription (RT)-PCR assay for fast and sensitive detection of bacterial contamination of blood products. Methods: We investigated different protocols for an automated high-volume extraction method based on magnetic-separation technology for the extraction of bacterial nucleic acids from platelet concentrates (PCs). We added 2 model bacteria, Staphylococcus epidermidis and Escherichia coli, to a single pool of apheresis-derived, single-donor platelets and assayed the PCs by real-time RT-PCR analysis with an improved primer-probe system and locked nucleic acid technology. Co-amplification of human β2-microglobulin mRNA served as an internal control (IC). We used probit analysis to calculate the minimum concentration of bacteria that would be detected with 95% confidence. Results: For automated magnetic bead-based extraction technology with the real-time RT-PCR, the 95% detection limit was 29 × 103 colony-forming units (CFU)/L for S. epidermidis and 22 × 103 CFU/L for E. coli. No false-positive results occurred, either due to nucleic acid contamination of reagents or externally during testing of 1030 PCs. Conclusions: High-volume nucleic acid extraction improved the detection limit of the assay. The improvement of the primer-probe system and the integration of an IC make the RT-PCR assay appropriate for bacteria screening of platelets. © 2007 American Association for Clinical Chemistry.