Multisite binding of bacteriophages on lipopolysaccharides in <i>Escherichia coli</i> O157:H7 and the adaptive costs of phage resistance

<i>Escherichia coli</i> (<i>E. coli</i>) O157:H7 is a major foodborne pathogen and a critical global food safety concern. Bacteriophage (phage) therapy offers a promising, highly specific biological alternative to antibiotic treatment. However, the clinical application of phage therapy is frequently limited by the rapid emergence of bacterial resistance. In this study, we examined the interaction between <i>E. coli</i> O157:H7 strain EDL933 and two T4-like phages, assessing the adaptive costs incurred by host strains in developing phage resistance. Our results indicate that phage PSD2001 utilizes capsular polysaccharide and lipopolysaccharides as adsorption receptors, while phage PNJ212 targets outer membrane protein C (OmpC) as its adsorption receptor. Notably, both phage employ gp37-like protein as receptor-binding proteins, highlighting the diversity of receptors on EDL933 and the complexity of phage-host recognition mechanisms. Furthermore, this study identified the adaptive costs of phage resistance, including antibiotic susceptibility, biofilm formation ability, survival, and colonization abilities, in the environment. These findings deepen our understanding of phage-host interactions and offer valuable insights for the application of phage therapy.IMPORTANCEPhage therapy offers an innovative strategy to combat antibiotic-resistant bacterial infections. To address the challenge of phage-resistant strains, we can adopt two strategies: using phage cocktails targeting multiple bacterial receptors to delay resistance development; and implementing a 'phage shift' treatment strategy that exploits the adaptive trade-offs of phage-resistant bacteria. Our research provides insights into the phage receptor recognition mechanisms in <i>Escherichia coli</i> O157:H7, a major foodborne pathogen. We identified key target receptors, including bacterial capsular polysaccharide, lipopolysaccharides, and OmpC, and found that the receptor-binding strategies of these phages resemble those of the T4 phage tail fiber protein gp37. Additionally, we revealed the adaptive costs associated with bacterial resistance to phage, which can inform strategies to enhance phage therapy efficacy. In summary, our findings provide a theoretical foundation for the prevention and control of clinical <i>E. coli</i> O157:H7 strains.