Chemically modified and inactivated bacteria enable intra-biofilm drug delivery and long-term immunity against implant infections.

Bacterial biofilms, prevalent in human infections, present a major barrier to effective antibacterial therapy due to limited drug permeability and resistance. Here we introduce a 'trick-bacteria-with-bacteria' strategy that employs bacteria modified via calcium chloride treatment and antibiotic loading, followed by ultraviolet inactivation. These modified bacteria integrate selectively into biofilms of the same species, enabling targeted intra-biofilm drug release triggered by local pH and hydrogen peroxide. Species-specific integration is essential, as mismatched strains exhibit spatial segregation due to differences in surface adhesins and protein profiles. The strategy is effective against polymicrobial biofilms and demonstrated efficacy in treating biofilms formed by Staphylococcus aureus, Escherichia coli and Candida albicans. It also reinvigorates biofilm-associated macrophages by inducing the release of biofilm-derived l-arginine, enhancing immune responses. In vivo studies using subcutaneous and bone implant infection models showed stronger biofilm eradication and longer-term immunity in animals treated with modified bacteria compared with those treated with antibiotics, including resistance to re-infection. This approach could be adapted to modify infection-related bacteria from patients for personalized intra-biofilm drug delivery.