Identification of pathogenic bacteria in human blood using IgG-modified Fe₃O₄ magnetic beads as a sorbent and...

A method is described for fast identification of bacteria by combining (a) the enrichment of bacterial cells by using magnetite (Fe₃O₄) magnetic beads modified with human IgG (IgG@Fe₃O₄) and (b) MALDI-TOF MS analysis. IgG has affinity to protein A, protein G, protein L and glycans on the surface of bacterial cells, and IgG@Fe₃O₄. It therefore is applicable to the preconcentration of a range of bacterial species. The feasibility of the method has been demonstrated by collecting six species of pathogenic bacteria (Gram-positives: Staphylococcus aureus and Kocuria rosea; Gram-negatives: Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae and Pseudomonas aeruginosa). Bacteria with concentrations as low as 10 CFU·mL^-1 in spiked water samples were extracted by this sorbent with recovery rates of >50%. After enrichment, bacteria on the IgG@Fe₃O₄ sorbent were further identified by MALDI-TOF MS. Bacteria in concentrations as low as 10⁵ CFU in 100 μL of human whole blood can be identified by the method. Compared to other blood culture based tests, the culture time is shortened by 40% (from ~10 h to ~6 h), and the plate culture procedure (overnight) is avoided. After short blood culture, the enrichment and identification can be finished in one hour. The IgG@Fe₃O₄ is of practical value in clinical diagnosis and may be combined with other identification methods, e.g. PCR, Raman spectroscopy, infrared spectroscopy, etc. Graphical abstract A non-targeted, fast and sensitive assay for bacterial identification from human blood has been developed based on the enrichment of bacteria by IgG@Fe₃O₄ and identification by MALDI-TOF MS.