Characterization and therapeutic potential of DepZ57, a stable depolymerase targeting hypervirulent K57 Klebsiella...

Klebsiella pneumoniae (K. pneumoniae) is recognized as a significant opportunistic pathogen capable of infecting both humans and animals. The emergence of multidrug-resistant strains presents a severe challenge to current antimicrobial therapies, necessitating the development of alternative treatments such as bacteriophages and their encoded enzymes. In this study, a polysaccharide depolymerase, designated DepZ57, was identified, expressed, and characterized from the K57-specific lytic phage vB_Kp_Z57. Bioinformatic analysis indicated that DepZ57 is a hydrophilic protein with a theoretical isoelectric point of 6.27 and adopts a typical β-helix structure. The purified depolymerase exhibited high physicochemical stability across a broad pH range (2.0-11.0) and temperature range (4°C-70°C). In vitro, the K57 capsule was degraded by DepZ57 at a minimum effective concentration ranging from 0.04 to 0.4 μg/mL, which subsequently sensitized the bacteria to macrophage phagocytosis and complement-mediated serum killing. In a lethal systemic mouse infection model induced by intraperitoneal injection, a 100% survival rate was achieved following the administration of 50 μg of DepZ57, compared with a 60% survival rate observed with the phage treatment. Bacterial burdens were effectively reduced by both treatments. Notably, the bacterial loads in the blood, lungs, and liver were significantly decreased in the DepZ57 treatment group. Specifically, the bacterial load in the blood was completely eliminated, and the bacterial loads in the liver and lungs were reduced by more than 99%. Histopathological analysis confirmed that DepZ57 treatment effectively prevented hepatic necrosis and pulmonary inflammatory infiltration. Collectively, these findings demonstrate the in vivo efficacy and stability of DepZ57, suggesting it may represent a viable candidate for the control of K. pneumoniae infections.

The emergence of multidrug-resistant and hypervirulent Klebsiella pneumoniae represents a severe threat to human health and the dairy industry. Capsular polysaccharide (CPS) is the primary virulence factor that shields K. pneumoniae from host immune clearance, and the hypervirulent K57 serotype is frequently linked to severe invasive infections. Phage-derived depolymerases have emerged as promising antivirulence agents capable of specifically dismantling bacterial capsules without inducing bacterial resistance. Here, we characterized a novel, highly stable phage depolymerase, DepZ57, which exhibits robust tolerance to extreme pH and temperature conditions and specifically targets K57-type CPS. Distinct from the parental phage, DepZ57 provides full protection against lethal K57 K. pneumoniae infection in vivo and effectively alleviates infection-induced tissue damage. This work highlights the potential of phage depolymerases as stable, safe, and efficient nonantibiotic therapeutics for the prevention and control of hypervirulent K. pneumoniae infections.