Abstract
ABSTRACTIn order to identify pathogens rapidly and reliably, bacterial capture and concentration from large sample volumes into smaller ones are often required. Magnetic labeling and capture of bacteria using a magnetic field hold great promise for achieving this goal, but the current protocols have poor capture efficiency. Here, we present a rapid and highly efficient approach to magnetic labeling and capture of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria using cationized magnetoferritin (cat-MF). Magnetic labeling was achieved within a 1-min incubation period with cat-MF, and 99.97% of the labeled bacteria were immobilized in commercially available magnetic cell separation (MACS) columns. Longer incubation times led to more efficient capture, with S. aureus being immobilized to a greater extent than E. coli. Finally, low numbers of magnetically labeled E. coli bacteria (<100 CFU per ml) were immobilized with 100% efficiency and concentrated 7-fold within 15 min. Therefore, our study provides a novel protocol for rapid and highly efficient magnetic labeling, capture, and concentration of both Gram-positive and Gram-negative bacteria.IMPORTANCE Antimicrobial resistance (AMR) is a significant global challenge. Rapid identification of pathogens will retard the spread of AMR by enabling targeted treatment with suitable agents and by reducing inappropriate antimicrobial use. Rapid detection methods based on microfluidic devices require that bacteria are concentrated from large volumes into much smaller ones. Concentration of bacteria is also important to detect low numbers of pathogens with confidence. Here, we demonstrate that magnetic separation columns capture small amounts of bacteria with 100% efficiency. Rapid magnetization was achieved by exposing bacteria to cationic magnetic nanoparticles, and magnetized bacteria were concentrated 7-fold inside the column. Thus, bacterial capture and concentration were achieved within 15 min. This approach could be extended to encompass the capture and concentration of specific pathogens, for example, by functionalizing magnetic nanoparticles with antibodies or small molecule probes.
Highlights
Antimicrobial resistance (AMR) is a significant global challenge
We show the potential of cationized magnetoferritin to rapidly magnetize E. coli
Magnetic capture efficiency was investigated by incubating 0.6-ml water samples inoculated with approximately 108 CFU mlϪ1 E. coli for 1 to 30 min with 0.5 M cationized magnetoferritin (cat-MF) and passing the water samples through a magnetic cell separation (MACS) column
Summary
Antimicrobial resistance (AMR) is a significant global challenge. Rapid identification of pathogens will retard the spread of AMR by enabling targeted treatment with suitable agents and by reducing inappropriate antimicrobial use. Previous studies reported the use of magnetic nanoparticles with different surface functionalizations, such as amine and carboxyl groups [9, 10], or small molecules, such as vancomycin [8, 11] In all of these studies, a permanent magnet is placed against a vial containing the magnetized bacteria, which results in sedimentation of the cells. We propose a novel approach to capture and concentrate bacteria, which involves the use of cationic magnetic nanoparticles and commercially available magnetic cell separation (MACS) columns; the former enable ultrafast labeling [12], while the latter enhance the efficiency of capture and concentration. We demonstrate that magnetization and concentration of bacteria can be accomplished within 15 min using cationic SPIONs that rapidly attach to anionic domains on the cell surface [12] and MACS columns to subsequently capture and concentrate the magnetized bacteria with up to 100% efficiency
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