Therapeutic efficacy of a K1-specific bacteriophage against hypervirulent Klebsiella pneumoniae in a mouse infection model

: Klebsiella pneumoniae is an important opportunistic pathogen in both humans and animals. Controlling it has become increasingly difficult due to the rapid spread of antimicrobial resistance. In this study, we isolated and characterized a novel lytic bacteriophage, vB_Kp_Z1, and evaluated its therapeutic efficacy against K1-serotype K. pneumoniae . Host range analysis showed that vB_Kp_Z1 was strictly specific to K1 strains, as confirmed across multiple prevalent capsular types. The in vivo efficacy of vB_Kp_Z1 was assessed using intraperitoneal infection models in mice. Two hypervirulent K1 strains were used: a pigeon-derived strain (KP1897) and a human clinical strain (KP177). Phage treatment significantly improved survival compared with phosphate-buffered saline-treated controls. It provided complete protection in KP1897-infected mice and achieved an 87.5% survival rate in KP177-infected mice. In addition, phage administration markedly reduced bacterial loads in the blood, liver, and lungs, indicating effective control of systemic dissemination. These findings demonstrate that vB_Kp_Z1 is a K1-specific bacteriophage with therapeutic potential against hypervirulent K. pneumoniae , including strains from different host species.