Foodborne bacteria play an important role in the spread of antibiotic resistance and complicate treatment processes. Regarding antibiotic resistance, extended-spectrum beta-lactamase (ESBL)-producing E. coli and carbapenem-resistant Enterobacterales are among the issues highlighted by the WHO. In this study, 200 ready-to-eat stuffed mussels from Istanbul were collected from various sales points (street vendors, kiosks, and restaurants) in 2024, and the presence of ESBL-producing E. coli was investigated. A total of 3.5% (7/200) E. coli was confirmed by PCR with 16S rRNA-specific primer. Antibiotic susceptibilities of the isolates to cefotaxime, ceftazidime, amoxicillin-clavulanic acid, meropenem, and ampicillin were measured by disk diffusion method. ESBL production in E. coli isolates was investigated using a double disk synergy test for phenotypic confirmation and bla_OXA, bla_CTX-M, bla_SHV, and bla_TEM gene presence by mPCR, and one isolate was found to contain the bla_TEM gene. The disk diffusion test and PCR investigated related carbapenem resistance, and bla_NDM-1, bla_OXA-48, bla_VIM, and bla_IMP genes were not observed in any isolate. This study is the first report of ESBL-producing E. coli isolate from ready-to-eat stuffed mussels in Türkiye. The presence of foodborne ESBL-producing E. coli threatens public health. It is necessary for food safety and global health to report the threats detected, especially in ready-to-eat products, and to take necessary measures.