Received on March 29, 2006
Accepted on October 18, 2006

Automation and Analytical Techniques

High-Volume Extraction of Nucleic Acids by Magnetic Bead Technology for Ultrasensitive Detection of Bacteria in Blood Components

¹ Institut für Laboratoriums und Transfusionsmedizin, Herz und Diabeteszentrum Nordrhein-Westfalen, Universitätsklinik der Ruhr-Universität Bochum, Bad Oeynhausen, Germany;

^* To whom correspondence should be addressed. E-mail: jdreier{at}hdz-nrw.de.

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. Coamplification of human ₂-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 x 10³ colony-forming units (CFU)/L for S. epidermidis and 22 x 10³ CFU/L for E. coli. No false-positive results occurred, either due to nucleic acid contamination of reagents or externally during testing of 342 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.