Rapid concentration of bacterial targets from dilute solutions to improve subsequent PCR detection is investigated in this study. Submicron (average size 500nm) superparamagnetic anion-exchangers (SiMAG-DEAE) were used successfully to concentrate target bacteria from very dilute solutions. A mass-balance model predicted that for Escherichia coli, the extent of cell concentrating increases almost linearly with increasing sample/SiMAG volume ratio up to about 2000, accompanied by only a slight decrease in the capture efficiency (<10%). Our experimental data generally support this analysis in that the SiMAG beads concentrated bacterial targets by two to three orders of magnitude using a sample/bead volume ratio of about 1000, and lowered the PCR detection limit to a level of 10(2)CFU/mL, from 10(4) to 10(5)CFU/mL without concentrating. Several target bacteria can be concentrated concurrently and detected via multiplex PCR, as illustrated using E. coli and Agrobacterium tumefaciens as model bacteria. Finally, concentration and detection of bacteria in fresh produce samples were demonstrated. The integration of submicron magnetic ion exchangers and PCR detection provides an appealing alternative to immunomagnetic separation/PCR in improving pathogen detection.
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