Antimicrobial Gold Nanoclusters Eradicate Escherichia coli Biofilms and Are Nontoxic by Oral Administration

Escherichia coli biofilms are a major causative agent of many intestinal infections, and there is ongoing research aimed at E. coli biofilm eradication. Gold nanoclusters (AuNCs) conjugated with various surface ligands have been extensively investigated for antimicrobial properties and provide a potential solution. There is little known about their in vivo safety because current standards of nanosafety research involve incubation of AuNCs with cells in vitro to confirm biocompatibility. In addition to systemic administration, nanosafety research on AuNC-based antimicrobials designed to treat gastrointestinal infections must also consider the potential for inducing gastrointestinal disorders. We report the design and application of two AuNCs coated with either hydroxyl (AuNC@PEG-OH)- or amine (AuNC@PEG-NH₂)-functionalized poly­(ethylene glycol), which enables the eradication of E. coli biofilms. Gastrointestinal safety of AuNC@PEG-OH and AuNC@PEG-NH₂ was evaluated in healthy mice up to 35 days after administration by oral gavage at a dose of 10 mg/kg (or 1 mg/mL) daily for 14 days. No changes were detected in the histopathology of major organs, serum chemistry, hematology, and feces. Thus, oral administration of AuNCs is unlikely to be of concern for systemic toxicity or in the induction of gastrointestinal illnesses. Further studies on increasing time exposure and doses are necessary to determine whether toxicity occurs at higher doses or whether there is no adverse effect limit.