The isotachophoretic analysis of different bacterial strains was studied using capillaries with different internal diameters from 50 to 250 mu m. Several injection modes were investigated and compared in order to improve the limit of detection of bacteria by capillary isotachophoresis. A system suitability test obtained from the separation voltage was developed to ensure reliable results. As expected, the use of wider bore capillaries improved the analytical sensitivity of the isotachophoretic method when compared to the 50 mu m capillary. With the optimized conditions, the isotachophoretic method presented in this work allows the quantification of Erwinia carotovora (Gram negative bacteria) with a limit of detection as low as similar to 3000 cells mL(-1). The proposed methodology does not require any additive in the electrolyte such a fluorescent or chromophoric dye to reach these limits of detection. (C) 2012 Elsevier BM. All rights reserved.