Characterization of a Novel Phage HZJ33 and Its Application in the Treatment of Carbapenem-Resistant Klebsiella pneumoniae Infection

Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a critical global public health challenge. Phages are regarded as promising alternatives to antibiotics. In this study, a novel lytic phage, HZJ33, was isolated from the clinical CRKP strain KP703. Transmission electron microscopy (TEM) revealed that HZJ33 possessed an icosahedral head and podovirus morphotype. HZJ33 achieved optimal infectivity at a multiplicity of infection (MOI) of 0.01, with a latent period of 10 min and a burst size of 4.65 × 10⁴ PFU/cell. It lysed 40% of tested clinical CRKP isolates (12/30). The endotoxin level released from bacterial lysis mediated by phage HZJ33 was well below the established safety threshold and exhibited no detectable cytotoxicity. Whole-genome analysis confirmed the absence of virulence and antibiotic resistance genes. In vitro, HZJ33 suppressed KP703 growth curves within 10 h. In the Galleria mellonella infection model, HZJ33 treatment at an MOI of 100 increased the larval survival rate to 75%, compared to 25% in the infected negative control group (1 × 10⁷ CFU/mL). These findings identify HZJ33 as a lytic phage with a broad host range, high stability, favorable safety, and strong antibacterial activity in vitro and in vivo, supporting its potential for CRKP therapy.