Escherichia coli has been used as an indicator of the fecal contamination of water and food, identifying potential health hazards. In this study, an E. coli-specific bacteriophage, T4, was used to detect E. coli bacteria. The T4 phage small outer capsid (SOC) protein was used to present green fluorescent protein (GFP), an easily detectable marker protein, on the phage capsid. To inactivate phage lytic activity, we used the T4e(-) phage, which does not produce the lysozyme responsible for host cell lysis. Infection of E. coli K12 cells with the GFP-labeled T4e(-) phage (T4e(-)/GFP) enabled the visualization and distinction of E. coli K12 cells from T4 phage-insensitive cells, Pseudomonas aeruginosa. Prolonged incubation of E. coli K12 cells with the T4e(-)/GFP phage did not lead to cell lysis. Propagation of T4e(-)/GFP in host cells increased the intensity of green fluorescence, making the distinction of E. coli cells from other cells simple and effective. This method enables the rapid, conclusive quantitation of E. coli cells within an hour.