Online Concentration of Bacteria from Tens of Microliter Sample Volumes in Roughened Fused Silica Capillary with Subsequent Analysis by Capillary Electrophoresis and Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry

This study presents a timely, reliable, and sensitive method for identification of pathogenic bacteria in clinical samples based on a combination of capillary electrophoresis with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. In this respect, a part of a single-piece fused silica capillary was etched with supercritical water with the aim of using it for static or dynamic cell-surface adhesion from tens of microliter sample volumes. The conditions for this procedure were optimized. Adhered cells of Staphylococcus aureus (methicillinsusceptible or methicillin-resistant) and of Pseudomonas aeruginosa were desorbed and preconcentrated from the rough part of the capillary surface using transient isotachophoretic stacking from a high conductivity model matrix. The charged cells were swep and separated again in micellar electrokinetic chromatography using a nonionogenic surfactant. Static adhesion of the cells onto the roughened part of the capillary is certainly volumetric limited. Dynamic adhesion allows the concentration of bacteria from 100 mu L volumes of physiological saline solution, bovine serum, or human blood with the limits of detection at 1.8 x 10(2), 1.7 x 10(3), and 1.0 x 10(3) cells mL(-1), respectively. The limits of detection were the same for all three examined bacterial strains. The recovery of the method was about 83% and it was independent of the sample matrix. A combination of capillary electrophoresis with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry required at least 4 x 103 cells mL-1 to obtain reliable results. The calibration plots were linear (R-2 = 0.99) and the relative standard deviations of the peak area were at most 2.2%. The adhered bacteria, either individual or in a mixture, were online analyzed by micellar electrokinetic chromatography and then collected from the capillary and off-line analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry without interfering matrix components.