This article describes electro-optical (EO) characterization of biospecific binding between Escherichia coli XL-1 and phage M13K07. The electro-optical analyzer (ELUS EO), which has been developed at the State Research Center for Applied Microbiology, Obolensk, Russia, was used as the basic instrument for electro-optical measurements. The operating principle of the analyzer is based on the polarizability of microorganisms, which depends strongly on their composition, morphology, and phenotype. The principle of analysis of the interaction of E. coli with phage M13K07 is based on recording changes in the optical parameters of bacterial suspensions. The phage–cell interaction includes the following stages: phage adsorption on the cell surface, entry of viral DNA into the bacterial cell, amplification of phage within the infected host, and phage ejection from the cell. In this work, we used M13K07, a filamentous phage of the family Inoviridae. Preliminary study had shown that combination of the EO approach with a phage as a recognition element has excellent potential for mediatorless detection of phage–bacteria complexes. The interaction of E. coli with phage M13K07 induced a strong and specific electro-optical signal as a result of substantial changes in the EO properties of the E. coli XL-1 suspension infected by phage M13K07. The signal was specific in the presence of foreign microfloras (E. coli K-12 and Azospirillum brasilense Sp7). Integration of the electro-optical approach with a phage has the following advantages: (1) bacteria from biological samples need not be purified, (2) the phage infection of bacteria is specific, (3) exogenous substrates and mediators are not required for detection, and (4) it is suitable for any phage–bacterium system when bacteria-specific phages are available.