Previously, Escherichia coli harboring the codon-optimized 3D8scFv gene (E. coli 3D8scFv) was developed as a feed additive for use in preventing norovirus infection. Here, we evaluated whether the 3D8scFv gene affects the colonization of E coli when E. coli 3D8scFv passes through the mouse gastrointestinal tract. To determine the colonization ability of E. coli 3D8scFv, E. coli cells with or without the 3D8scFv gene were fed to mice. Total DNA was extracted from the animals' stools, stomach, small intestine and colon. All samples were amplified using 3D8scFv gene-specific primer sets. E. coli 3D8scFv begins to be excreted 1 h after feeding and that all E. coli 3D8scFv cells were excreted between 12 and 24 h after the last feeding of the cells. The previously measured gastrointestinal transit time of the mice was between 8 h and 22 h. The results of this study therefore show that E. coli 3D8scFv cannot colonize the gastrointestinal tracts of mice. In addition, if the purified 3D8 scFv protein is used as a feed additive, any associated E. coli 3D8scFv bacteria will not colonize the gastrointestinal tracts of the livestock. Thus, this feed additive meets the safety assessment criteria for the commercial use of bacteria.