Focusing and Mobilization of Bacteria in Capillary Electrophoresis

An isotachophoretic method has been developed for mobilizing and focusing bacteria. This allows quantification and detection of bacteria in a narrow zone. Very good linearity was obtained for Micrococcus lysodeikticus (also called Micrococcus luteus, studied as a model of Gram+ bacteria) in the range of 0.4 x 10(8) cells/mL to 2.9 x 10(8) cells/mL, with correlation coefficients for peak height and peak area as a function of cell concentration of 0.999 and 0.998, respectively. This method is usable on both bare and hydroxypropyl cellulose coated fused silica capillaries. The best results were obtained using 13.6 mM Tris, 150 mM boric acid as terminating electrolyte, and 4.5 mM Tris, 50 mM boric acid, and 3.31 mM HCl as leading electrolyte. With a 33.5 cm x 100 mu m i.d. capillary, short migration times were obtained while maintaining very low electrical current in order to minimize any Joule heating and lysis of the bacteria. A UV area imaging detector (ActiPix D100, Paraytec) was used with a 109 cm x 100 mu m i.d. capillary having three loops and four detection windows to monitor the migration behavior of M luteus and to show the stability of the zone of the focused bacteria along the capillary. Similar results were obtained for Erwinia carotovora (a model of Gram bacteria), and for Enterobacter cloacae and Vibrio splendidus.