Phage-conjugated chlorin e6: A strategy overcoming phage resistance in biofilm eradication and wound infection therapy of carbapenem-resistant Acinetobacter baumannii

Abstract

Carbapenem-Resistant Acinetobacter baumannii (CRAB) frequently causes biofilm-related infections that can exhibit extreme resistance to antibiotic therapy. Phage therapy shows promise as an alternative treatment, yet bacteria may develop resistance to it with prolonged use. Phage-photosensitizer combination therapy represents a novel antimicrobial strategy. This study aims to evaluate the efficacy of chlorin e6-functionalized phage in eradicating biofilms and treating CRAB infections, and to assess its sustained after effect following the emergence of phage resistance. The A. baumannii phage (ABP)-chlorin e6 conjugate (ABP-Ce6) was successfully synthesized and characterized. It preserved the phage's absorptive capacity and lytic activity while enhanced reactive oxygen species (ROS) production. Moreover, ABP-Ce6 demonstrated remarkable antibacterial activity comparable to ABP while exceeding that of Ce6, and showed superior performance in both inhibiting biofilm formation and disrupting existing biofilms in CRAB Ab1513. Significantly, although ABP exhibited no efficacy against the phage-resistant CRAB Ab1513-BIM12 due to its inability to achieve irreversible adsorption, the ABP-Ce6 maintained potent antibacterial and biofilm ablation effects against this strain, outperforming free Ce6. This sustained efficacy arises from ABP's reversible adsorption, which still enables proximity-driven Ce6 delivery to the target bacteria. In vivo, the ABP-Ce6 significantly enhanced mice wound healing for infections caused by CRAB Ab1513 and Ab1513-BIM12. In conclusion, ABP-Ce6 exhibits significant efficacy as a therapeutic agent against CRAB infections even after the bacteria develop resistance to phage therapy. This novel strategy may serve as a hopeful complementary strategy to phage therapy, thereby reducing delays in screening for new therapeutic phages.