Isolation, Characterization, and Anti-Biofilm Activity of a Novel Kaypoctavirus Against K24 Capsular Type, Multidrug-Resistant Klebsiella pneumoniae Clinical Isolates

<b>Background/Objectives</b>: The significant outbreak of multidrug-resistant <i>Klebsiella pneumoniae</i> has emerged as a primary global concern associated with high morbidity and mortality rates. Certain strains of <i>K. pneumoniae</i> are highly resistant to most antibiotics available in clinical practice, exacerbating the challenge of bacterial infections. <b>Methods</b>: Phage vB_KpnP_PW7 (vKPPW7) was isolated and characterized. Its morphology, stability, adsorption rate, one-step growth curve, lytic activity, whole-genome sequence analysis, and antibacterial and antibiofilm activities were evaluated. <b>Results</b>: The virulent phage has a 73,658 bp linear dsDNA genome and was classified as a new species of the genus <i>Kaypoctavirus</i>, subfamily <i>Enquatrovirinae</i>, and family <i>Schitoviridae</i>. Phage vKPPW7 has a high adsorption rate, a short latent period, and a large burst size. The phage showed activity against 18 <i>K. pneumoniae</i> isolates with the K24 capsular type but was unable to lyse <i>K. pneumoniae</i> isolates whose capsular type was not classified as K24. Additionally, phage vKPPW7 demonstrated strong stability across various temperatures and pH values. The phage exhibited antibacterial activity, and scanning electron microscopy (SEM) confirmed its ability to lyse MDR <i>K. pneumoniae</i> with the K24 capsular type. Furthermore, phage vKPPW7 effectively removed preformed biofilm and prevented biofilm formation, resulting in reduced biofilm biomass and biofilm viability compared to controls. The architecture of phage-treated biofilms was confirmed under SEM. <b>Conclusions</b>: These findings suggest that phage vKPPW7 holds promise for development as a therapeutic or biocontrol agent.