Molecules that mediate the invasion of mammalian cells are of significant interest for the development of targeted drug and gene therapies for cancer. A more rapid isolation procedure would benefit the discovery of unique tumor targeting epitopes that allow for internalization into cells. To address this need, a bacterial surface display methodology was developed to discover peptide sequences that bind to and mediate invasion into human breast carcinoma cells. Nonpathogenic E. coli expressing both an intracellular fluorescent protein and an outer member protein capable of displaying peptides as insertional fusions on their cell surface were used to screen peptide libraries. Selections using a gentamicin protection assay were shown to enrich three peptide sequences that allowed for the bacteria to be internalized into tumor cells, as measured using quantitative flow cytometry and verified using fluorescence microscopy. These results further demonstrate that fluorescent bacterial display peptide libraries provide a powerful tool for identifying optimal targeting ligands for therapeutic applications.