Identification of pathogenic bacteria in human blood using IgG-modified Fe3O4 magnetic beads as a sorbent and MALDI-TOF MS for profiling.

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.