Intracellular bacterial infections are difficult to treat, and in the case of Salmonella and related infections, can be life threatening. Antibiotic treatments for intracellular infections face challenges including cell penetration and intracellular degradation that both reduce antibiotic efficacy. Even when treatable, the increased dose of antibiotics required to counter infections can strongly impact the microbiome, compromising the native roles of beneficial non-pathogenic species. Bioorthogonal catalysis provides a new tool to combat intracellular infections. Catalysts embedded in the monolayers of gold nanoparticles (nanozymes) bioorthogonally convert inert antibiotic prodrugs (pro-antibiotics) into active species within resident macrophages. Targeted nanozyme delivery to macrophages was achieved through mannose conjugation and subsequent uptake VIA the mannose receptor (CD206). These nanozymes efficiently converted pro-ciprofloxacin to ciprofloxacin inside the macrophages, selectively killing pathogenic Salmonella enterica subsp. enterica serovar Typhimurium relative to non-pathogenic Lactobacillus sp. in a transwell co-culture model. Overall, this targeted bioorthogonal nanozyme strategy presents an effective treatment for intracellular infections, including typhoid and tuberculosis.

Biofilm infections are a global public health threat, necessitating new treatment strategies. Biofilm formation also contributes to the development and spread of multidrug-resistant (MDR) bacterial strains. Biofilm-associated chronic infections typically involve colonization by more than one bacterial species. The co-existence of multiple species of bacteria in biofilms exacerbates therapeutic challenges and can render traditional antibiotics ineffective. Polymeric nanoparticles offer alternative antimicrobial approaches to antibiotics, owing to their tunable physico-chemical properties. Here, we report the efficacy of poly(oxanorborneneimide) (PONI)-based antimicrobial polymeric nanoparticles (PNPs) against multi-species bacterial biofilms. PNPs showed good dual-species biofilm penetration profiles as confirmed by confocal laser scanning microscopy. Broad-spectrum antimicrobial activity was observed, with reduction in both bacterial viability and overall biofilm mass. Further, PNPs displayed minimal fibroblast toxicity and high antimicrobial activity in an in vitro co-culture model comprising fibroblast cells and dual-species biofilms of Escherichia coli and Pseudomonas aeruginosa. This study highlights a potential clinical application of the presented polymeric platform.