The pH dependences of electrokinetic potentials (EKP) of the cells of two Escherichia coli K-12 strains (D21 and JM 103) with known lipopolysaccharide (LPS) core composition have been determined by the method of microelectrophoresis. At pH 4.6–5.2, the negative surface charge of the cells with Re core LPS was reliably higher. It was shown that the interaction of bacteria with lysozyme results in a decrease of optical density of suspensions due to higher sensitivity of the cells with complete LPS core to hypotonic shock. LPS release from bacterial cell wall depended also on bacterial LPS core composition and increased with LPS core extension. Electrokinetic measurements and the study of the interaction of cells with lysozyme suggest that higher negative surface charge of E. coli JM 103 cells (Re type LPS) is associated with higher quantity and density of LPS packing in the cell wall as compared with the cells of E. coli D21 (Ra type LPS).