The Fabrication of Protein Carriers for Intracellular Delivery of Antibiotics Against Intracellular Bacterial Infection

Bacterial infections pose a serious threat to human health, and antibiotics remain the first-line therapeutic agents in clinical practice. However, the vast majority of antibiotics lack the ability to penetrate cell membranes, which severely limits the number of clinically available options for treating intracellular bacterial infections. Developing efficient intracellular antibiotic delivery strategies is therefore of considerable clinical significance, both for reducing antibiotic dosage and for expanding the repertoire of drugs applicable to intracellular infections. To address this challenge, we constructed a protein-based delivery platform mediated by a cell-penetrating miniprotein for efficient intracellular antibiotic delivery. In this system, bovine serum albumin (BSA), which possesses broad antibiotic-binding capability, was employed as the drug carrier, while the cell-penetrating miniprotein ZF5.3, which is capable of endosomal escape, served as the transmembrane delivery mediator. ZF5.3 was conjugated to BSA via a bioorthogonal reaction, and ceftriaxone (CRO) was selected as the model antibiotic to construct a nanoscale delivery system. The binding interaction between CRO and BSA was characterized using UV-Vis, HPLC, and molecular docking techniques. The assembly of the ZF5.3–BSA delivery platform was confirmed by UV-Vis absorption spectroscopy and gel electrophoresis. Intracellular delivery efficiency was evaluated by confocal fluorescence imaging and flow cytometry, and the results demonstrated that ZF5.3 conjugation enhanced intracellular protein delivery efficiency by over 5-fold. Fluorescence co-localization analysis revealed that ZF5.3-mediated cargo is mainly distributed in the cytoplasm and does not completely co-localize with lysosomal markers, suggesting its ability to effectively escape from lysosomes. An intracellular infection model using Staphylococcus aureus was established. Colony-forming unit (CFU) counting experiments confirmed that the delivery system significantly enhanced the intracellular antibacterial activity of ceftriaxone. CCK8 cytotoxicity assays confirmed that the system is non-toxic to cells.