Phages ZC01 and ZC03 require type-IV pilus for infection and have a potential for therapeutic applications.

There has been a growing interest in bacteriophages as therapeutic agents to treat multidrug-resistant bacterial infections. The present work aimed at expanding the microbiological and molecular characterization of lytic phages ZC01 and ZC03 and investigating their efficacy in the control of infection in an invertebrate animal model. These two phages were previously isolated from composting using strain PA14 as the enrichment host and had their genomes sequenced. ZC01 and ZC03 present, respectively, siphovirus and podovirus morphotypes. ZC01 was recently classified into the genus , while ZC03 belongs to genus of the N4-like viruses. Through proteomics analysis, we identified virion structural proteins of ZC01 and ZC03, including a large virion-associated RNA polymerase that is characteristic of N4-like viruses, some hypothetical proteins whose annotation should be changed to virion structural proteins and a putative peptidoglycan hydrolase. Phages ZC01 and ZC03 exhibit a limited yet distinct host range, with moderate to high efficiency of plating (EOP) values observed for a few clinical isolates. Phage susceptibility assays in PA14 mutant strains point to the type-IV pilus (T4P) as the primary receptor for phages ZC01 and ZC03, and the major pilin (PilA) is the T4P component recognized by these phages. Moreover, both phages significantly increase survival of larvae infected with PA14 strain. Taken together, these results underpin the therapeutic potential of these phages to treat infections by and lay the groundwork for a more detailed investigation of phage-bacteria-specific recognition mechanisms.IMPORTANCEPhage therapy is gaining increasing interest in cases of difficult-to-treat bacterial human infections, such as carbapenem-resistant . In this work, we investigated the molecular mechanism underlying the interaction of the lytic phages ZC01 and ZC03 with the highly virulent PA14 strain and their efficacy to treat PA14 infection in larvae, a commonly used invertebrate model for phage therapy. We depicted the protein composition of ZC01 and ZC03 viral particles and identified pilin A, the major component of type-4 pilus, as the receptor recognized by these phages. Our findings indicate that phages ZC01 and ZC03 may be further used for developing therapies to treat multidrug-resistant infections.