A plasmid encoding a fusion protein (4TS-bccp87) composed of a thermostable mutant of the Luciola mingrelica firefly luciferase (4TS) and 87 carboxy-terminal amino acid residues of the biotin-binding domain (bccp87) from E. coli was constructed using genetic-engineering techniques. It was established that fusion-protein expression in BL21(DE3) E. coli resulted in 60% of the biotinylated form. The catalytic properties, thermostability, and bioluminescence spectra of the fusion protein were shown to be similar to that of the initial luciferase. The possibility of using the streptavidin-biotinylated luciferase complex for defining the Salmonella typhimurium cell concentration in the range from 104 to 5 × 106 CFU/ml by enzyme immunoassay was shown.