Bacterial Receptors but Not Anti-Phage Defense Mechanisms Determine Host Range for a Pair of Pseudomonas aeruginosa Lytic Phages.

Limited phage host range remains one of the obstacles to the widespread use of phage therapy against bacterial infections. Here, we perform a genome-wide association study (GWAS) using Pseudomonas aeruginosa clinical isolates collected from people with cystic fibrosis (pwCF) to identify bacterial genes associated with resistance or susceptibility to two lytic phages, OMKO1 and LPS-5, recently used in a clinical trial in pwCF. Results were validated with transposon mutagenesis experiments and functional assays. Genes associated with flagellum assembly and lipopolysaccharide biosynthesis are essential for infection by OMKO1 and LPS-5, respectively, consistent with functional studies implicating these molecules as receptors for these phages. Notably, the presence of bacterial genes encoding phage defense mechanisms is not predictive of phage susceptibility. Instead, the relative abundance of defense elements is associated with the number of temperate phages within bacterial genomes. Together, our findings highlight the central role of receptors in determining phage host range.