Mass spectrometry of serum polypeptides of Enterococcus faecium bloodstream infection in mice

Objective To analyze the serum polypeptide fingerprints of Enterococcus faecium (E. faecium) bloodstream infection in mice at different time points using matrix assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-FOF MS), screen differential polypeptide peaks, and create a corresponding diagnostic model and look for new markers. Methods Ninety ICR mice were used to establish E. faecium bloodstream infection model (including 10 mice as normal control group with PBS injection, and 80 mice as the infection group with 1/2 LD50 E. faecium injection in a volume of 0.1 ml/10 g by the intravenous tail). Blood samples were collected at 8 time points (1, 3, 6, 12, 24, 48, 96 and 128 h), and tested for IL-1α, IL-1β and IL-6 detection. Serum samples were then purified with weak cation magnetic beads, the serum polypeptide profiling was recognized by MALDI-TOF MS and BioExplorer software between infection group and normal control group. Amino acid sequences of the candidate polypeptides were identified by nano-liquid chromatography electrospray ionization-tandem mass spectrometry (nano- LC/ESI–MS/MS). Results After infected with E. faecium, the mice showed abnormal behaviors compared with the normal control group, including listless and reduced activity; IL-1α was down-regulated, while IL-1β and IL-6 were up-regulated. A total of 102 polypeptide peaks were detected by fingerprints analysis. Screening on the basis of 5 times difference in content in both infection group and control group, 8 polypeptides were higher in infection group than those in control group (P