Isolation and engineering of antimicrobial peptides targeting pathogenic Escherichia coli and Salmonella of poultry

Abstract Antimicrobial-resistant (AMR) infections impose significant economic, welfare and zoonotic disease burdens on food production worldwide. In poultry, AMR pathogens such as Escherichia coli and monophasic Salmonella Typhimurium are particularly concerning and require alternative strategies for their control. Here, a phage display 16mer-peptide library was produced and panned using next generation sequencing selection to identify peptides that were enriched against E. coli and S. Typhimurium. Binding peptides were then screened for antimicrobial activity in minimum inhibitory concentration and/or minimum bactericidal concentration assays. Fifty-seven peptides were enriched during phage display panning and five displayed antimicrobial activity in the low µM range. The incorporation of in silico antimicrobial peptide (AMP) prediction tools to analyse enriched peptides could improve efficiency: identifying four AMPs from screening only thirteen peptides. Peptides were assessed as homodimers and heterodimers, the latter coupled peptides isolated by phage display with truncated Cathelicidin-BF. Dimers were shown to display altered potency and/or specificity compared to the constituent monomers. Furthermore, it was shown that the relative activity of the peptides could change in mixed cultures compared to monocultures. This was apparent for the Cathelicidin-BF monomer and (GWG)-(Cathelicidin-BF) heterodimer that both displayed preferential killing of E. coli only in mixed-cultures.