Molecular characterization of multi-drug resistance Escherichia coli O157:H7 from calf feces and cow milk in Bangladesh

Escherichia coli O157:H7 is one of the several zoonotic bacteria that causes food-borne disease, has socioeconomic sphere and public health impacts. Cattle are an important reservoir of E. coli O157:H7, and shed in their feces as well as contaminate animal-origin food products, sometimes leading to transmission to humans. This study investigated the prevalence, antimicrobial resistance (AMR) patterns, and genomic characteristics of E. coli O157:H7 from calf fecal swabs and cow milk in Bangladesh. A total of 290 samples were collected from dairy cattle of different areas, screened using real-time PCR and selective culture, followed by phenotypic and genotypic AMR profiling, and whole‑genome sequencing with comparative genomics. Overall, 20% of samples tested positive in real-time PCR with a higher prevalence in fecal samples (24.8%) than milk (7.5%). All E. coli O157:H7 isolates were susceptible to amoxicillin‑clavulanate, azithromycin, tetracycline, and gentamicin; however, 50% were multidrug‑resistant (MARI up to 0.33). Genomic analysis revealed the presence of stx2 and eae virulence genes, and multiple AMR genes including acrA, acrS, emrR, emrB, and marA. This also explores the E. coli O157:H7 belongs to lineage ST11 which harbor mobile genetic elements, multiple plasmid types and stx-converting prophage, and showed high genomic similarity to outbreak‑associated Sakai strain. The co‑occurrence of high‑risk virulence genes, multidrug resistance, and an epidemic lineage highlights an urgent need for integrated genomic surveillance, improved hygiene, and responsible antimicrobial use within a One Health framework to mitigate zoonotic transmission of E. coli O157:H7 through the dairy value chain.