Elucidating Key Steps of Pseudomonas Aeruginosa Infection by DEV Lytic Phage for Phage Therapy

Phage therapy is a promising treatment for infections caused by antibiotic resistant bacteria including Pseudomonas aeruginosa (Pa). Studying the biology of phages for therapy is important to make it safe and effective. We are currently studying the adsorption mechanism of DEV, a component of a four-phage cocktail (CK4) effective against Pa in animal models1. DEV enjoys a two-receptor adsorption mechanism, with the O-antigen moiety of lipopolysaccharide (LPS) as first receptor2. DEV gp53 long tail fiber is required for the infection of strains producing the O-antigen, but dispensable to infect galU mutants producing LPS without the O-antigen. While further experiments are required, current findings strongly suggest LptD serves as the secondary receptor for DEV phage. We found that galU lptD double mutants are DEV resistant and have decreased adsorption, which improved upon lptD mutation complementation. LPS analysis showed similar patterns between galU lptD DEV-resistant mutant and DEV-susceptible galU mutant, suggesting that the mutation in LptD does not dramatically affect LPS composition or tansport. Interestingly, the expression of Pa lptD in Escherichia coli, which is not susceptible to DEV and distantly related to Pa, promoted DEV adsorption, supporting the hypothesis that LptD is used as receptor by DEV.