Protective effects of recombinant depolymerase Dep44 against K64-CRKP-induced pulmonary infection in a murine infection model

BACKGROUND: Carbapenem-resistant Klebsiella pneumoniae (CRKP) represents a critical public health challenge due to limited treatment options. Among CRKP serotypes, K64 has emerged as the most prevalent in China. This study aimed to isolate and characterize a phage specific for K64-CRKP and assess the protective efficacy of the depolymerase derived from this phage against CRKP-induced pulmonary infection in murine infection model, thereby establishing a scientific foundation for depolymerase-based therapeutic interventions. In this study, we isolated phage vB_Kpn_HF1013 capable of lysing K64-CRKP from hospital sewage and constructed its depolymerase recombinant protein Dep44. The adjuvant anti-infective potential of the recombinant protein was subsequently validated in in vitro and vivo experiments. RESULTS: A K64-specific lytic phage, vB_Kpn_HF1013, was efficiently isolated from hospital wastewater. Dep44 effectively degraded the capsular polysaccharides of K64-CRKP without directly inhibiting bacterial growth. In vivo, Dep44 treatment significantly reduced pulmonary bacterial loads (P < 0.0001), mitigated histopathological lung damage, and suppressed inflammatory cytokine expression (Il6, Il1b). Transcriptomic analysis revealed upregulation of B-cell receptor-related genes and downregulation of proinflammatory pathways, including TNF and JAK-STAT signaling. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed significant downregulation of pathways linked to acute inflammation, tissue injury, and apoptosis. CONCLUSION: Dep44 exhibits robust capsule-depolymerizing activity and confers significant protection against K64-CRKP-induced lung infection in mice. These findings highlight its potential as a promising adjunct or alternative to antibiotic therapy for CRKP infections.