Main content area

Rapid analysis of Gram-positive bacteria in water via membrane filtration coupled with nanoprobe-based MALDI-MS

Li, Shuping, Guo, Zhongxian, Wu, Hui-Fen, Liu, Ying, Yang, Zhaoguang, Woo, Chee Hoe
Analytical and bioanalytical chemistry 2010 v.397 no.6 pp. 2465-2476
Bacillus cereus, Bacillus subtilis, Enterococcus faecium, Gram-negative bacteria, Gram-positive bacteria, Staphylococcus aureus, aqueous solutions, desorption, detection limit, filtration, ionization, magnetic separation, magnetite, mass spectrometry, nanoparticles, rapid methods, tap water, water analysis, water reservoirs
Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS) is challenging when it is directly applied to identify bacteria in water. This study demonstrates a rapid, sensitive, and selective technique for detection of Gram-positive bacteria in water. It involves a combination of membrane filtration (MF) and vancomycin-conjugated magnetite nanoparticles (VNPs) to selectively separate and concentrate Gram-positive bacteria in tap water and reservoir water, followed by rapid analysis of the isolates using whole-cell MALDI-MS. VNPs specifically recognize cells of Gram-positive bacteria, which serves as a basis for affinity capture of target Gram-positive bacteria. A two-step procedure of surface modification of bare magnetite nanoparticles was applied to synthesize VNPs. MF prior to VNP-based magnetic separation can effectively increase the enrichment factor and detection sensitivity and reduce time-consuming culture steps and the matrix effect for analysis of bacteria in MALDI-MS. The enrichment factor for the MF-VNP technique is about 6 × 10⁴. A variety of bacteria, including Staphylococcus aureus, Bacillus subtilis, Bacillus cereus, and Enterococcus faecium, were successfully analyzed from aqueous solutions and their mixtures with Gram-negative bacteria. The optimal conditions of the VNP/MALDI-MS technique, including selection of the MALDI matrix, the choice of cell-washing solution, and the VNP concentration, were also investigated. The capture efficiencies of Gram-positive bacteria with VNPs were 26.7-33.3%. The mass variations of characteristic peaks of the captured bacteria were within ±5 Da, which indicated good reproducibility of the proposed technique. The technique was applied to detect Gram-positive bacteria in tap water and reservoir water with an analysis time of around 2 h. The detection limit for Bacillus cereus, Enterococcus faecium, and Staphylococcus aureus was 5 × 10² cfu/ml for 2.0-l water samples. [graphic removed]