Enterohemorrhagic Escherichia coli (EHEC) O157:H7 causes life-threatening disease in humans, characterized by bloody diarrhea and, in severe cases, brain and kidney damage. Ruminants—especially cattle—serve as the primary reservoir, where the bacterium asymptomatically colonizes the recto-anal junction. Our previous research demonstrated a mucosal immune bias towards a Th1 profile, with antigen-specific CD4⁺ and CD8⁺ T-cell proliferation. Mathematical modeling in humans suggests that EHEC O157:H7 effector proteins have evolved mechanisms to reduce MHC Class I (MHCI) ligand density, allowing the pathogen to escape immune surveillance through impaired antigen presentation and CD8⁺ T-cell recognition. In our study, we identified EHEC O157 peptides presented on infected bovine epithelial cells using peptide elution and mass spectrometry. The results revealed that most eluted peptides were derived from structural proteins with only one bacterial peptide—derived from the translocator effector protein EspF—but it did not meet the predicted binding threshold for the expressed MHCI alleles. Notably, two MHCI ligands originated from Intimin, a key bacterial adhesion factor crucial for cattle colonization, where one overlapped with a known CD4⁺ T-cell epitope, representing a promising vaccine candidate. Our in vitro model, using a bovine epithelial cell line expressing BoLA-1*023:01 and autologous CD8⁺ T cells, showed that EHEC O157 suppresses antigen-specific CD8⁺ T-cell activation, suggesting that the bacterial-secreted effector interferes with peptide processing and/or MHCI loading. This study provides a novel insight into veterinary immunology, particularly in the context of extracellular pathogens. It highlights the importance of including both CD4⁺ and CD8⁺ T epitopes in rational vaccine design—an often underexplored strategy for extracellular pathogens like EHEC O157. By integrating immunopeptidomics, in silico prediction, and a bovine in vitro model, we establish a basis for next-generation vaccines to eliminate persistent infections and limit zoonotic transmission.