Bacterial ghosts for targeting delivery and subsequent responsive release of ciprofloxacin to destruct intracellular bacteria

Macrophages are one of the main host cells of intracellular pathogens and the elimination of intracellular bacteria (ICBs) relies on sufficient antibiotic concentrations inside infected macrophages. Current antibiotic delivery systems are confronted with challenges in identification of infected macrophages from normal cells and responsive release to intracellular cues. In the current study, bacterial ghosts (BGs) are constructed from E. coli Nissle 1917 (EcN) into an antibiotic-loading platform for destroying intracellular S. aureus. BGs show high ciprofloxacin (CIP) loading of 12.5% and desired scalability and reproducibility of preparations. BGs indicate 2.5-folds higher uptake efficiency into macrophages than live EcN, and maintain the immunogenicity to produce pro-inflammatory cytokines. CIP-loaded BGs (BG@Cip) are relatively stable in the extracellular space, while the accumulated release reaches over 80% within 4 h in response to the elevated intracellular lysozyme of infected macrophages. Compared with negligible effect of free CIP, the BG@Cip treatment reduces the ICB viabilities by 3 orders of magnitude. After intravenous administration, BG@Cip causes over 4 folds higher drug levels in liver and spleen than free CIP, suggesting the targeting ability of BGs to infected macrophages. Compared with no mice survival after 72 h of free CIP treatment, all the infected mice survive after BG@Cip treatment without obvious intumescentia and histopathological abnormalities in the infected tissues like liver, spleen and kidney. The BG@Cip treatment indicates no hematological toxicity and inhibits the hepatotoxicity and nephrotoxicity caused by S. aureus infection. It demonstrates the advantages of BGs as a feasible carrier of antibiotics with large loading capacity, high targeting efficiency, intracellular enzyme-responsive release and pro-inflammatory cytokine secretion, leading to a full destruction of ICB infections without any apparent side effects.