Characterization and genomic insights into bacteriophages Kpph1 and Kpph9 against hypervirulent carbapenem-resistant Klebsiella pneumoniae

The increasing incidence of infections attributed to hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKp) is of considerable concern. Bacteriophages, also known as phages, are viruses that specifically infect bacteria; thus, phage-based therapies offer promising alternatives to antibiotic treatments targeting Hv-CRKp infections. In this study, two isolated bacteriophages, Kpph1 and Kpph9, were characterized for their specificity against the Hv-CRKp K. pneumoniae NUHL30457 strain that possesses a K2 capsule serotype. Both phages exhibit remarkable environmental tolerance, displaying stability over a range of pH values (4-11) and temperatures (up to 50 degrees C). The phages demonstrate potent antibacterial and antibiofilm efficacy, as indicated by their capacity to inhibit biofilm formation and to disrupt established biofilms of Hv-CRKp. Through phylogenetic analysis, it has been revealed that Kpph1 belongs to the new species of Webervirus genus, and Kpph9 to the Drulisvirus genus. Comparative genomic analysis suggests that the tail fiber protein region exhibits the greatest diversity in the genomes of phages within the same genus, which implies distinct co-evolution histories between phages and their corresponding hosts. Interestingly, both phages have been found to contain two tail fiber proteins that may exhibit potential depolymerase activities. However, the exact role of depolymerase in the interaction between phages and their hosts warrants further investigation. In summary, our findings emphasize the therapeutic promise of phages Kpph1 and Kpph9, as well as their encoded proteins, in the context of research on phage therapy targeting hypervirulent carbapenem-resistant Klebsiella pneumoniae.