Enterotoxigenic Escherichia coli (ETEC) colonizes the intestine of young pigs causing severe diarrhoea and consequently bringing high producing costs. The rise of antibiotic selective pressure together with on-going limitation on their use demands news strategies to tackle this pathology. The pertinence of using phages to tackle this problematic is being explored, and in this work, the efficacy of a T4-like phage vB_EcoM_FJ1 (FJ1) in reducing the load of ETEC O9:H9 (Sta, F5/F41) was assessed. FJ1 has a 170,053 bp genome, and of the 270 coding sequences none corresponds to identified undesirable proteins, such as integrases or transposases. Envisaging the oral application to piglets, FJ1 was previously encapsulated on CaCO3/alginate. Assays were performed on 15-day cultures of the intestinal pig cell line IPEC-1 seeded in transwell inserts. Phage treatment occurred 2 hours after ETEC infection, when, in average, 5x105 CFU.cm-2 were adhered to cultured cells. Encapsulated phage provided reductions of, approximately, 2.3 Log CFU.cm-2 and 2.8 Log CFU.cm-2 on adhered bacteria, respectively 3 and 6 hours after administration. The repeated exposure of the host to FJ1 led to the emergence of phage-insensitive mutants, phenotype that brought fitness costs to the host strain: they were 70% more vulnerable to the pig complement system and less efficient in adhering to cultured cells (in about 90%). Overall, FJ1 is presented here as promising to fight against ETEC infections through oral administration to piglets.info:eu-repo/semantics/publishedVersio
