Bi2O3nanoparticles exhibit potent broad-spectrum antimicrobial activity and the ability to overcome Ag-, ciprofloxacin- and meropenem-resistance in P. aeruginosa: the next silver bullet of metal antimicrobials?Electronic supplementary information (ESI) available. See DOI: 10.1039/d1bm01844b

Antimicrobial resistance is a persistent threat to global public health. In order to combat the spread of pathogenic bacteria, numerous antimicrobial materials have been incorporated into wound dressings and medical devices such as implants and catheters. The most frequently utilized of these materials are Ag-salts and Ag-nanoparticles (AgNPs) due to their low minimum inhibitory concentrations (MICs) against common Gram-negative pathogenic bacteria such as P. aeruginosa. However, such Ag-based materials are limited to treating Gram-negative bacteria and prone to generating Ag-resistant phenotypes after only 7 consecutive exposures to these materials at a sub-inhibitory concentration. Here, we demonstrate α-Bi2O3NPs as potential replacements for such materials, i.e., α-Bi2O3NPs that exhibit potent broad-spectrum antibacterial activity (MIC = 0.75 μg mL−1against P. aeruginosa; MIC = 2.5 μg mL−1against S. aureus). Furthermore, these NPs are effective against Ag-resistant and carbapenem-resistant bacteria (MICs = 1.0 μg mL−1and 1.25 μg mL−1, respectively) and also show a synergistic effect with meropenem (mero) in P. aeruginosabacteria, allowing for the use of meropenem with smaller therapeutic doses (fractional inhibitory concentration = 0.45). Finally, unlike other materials that have been explored as effective antimicrobials, α-Bi2O3NPs do not contribute to the development of Bi-resistant phenotypes after 30 passages of consecutive exposure to a sub-lethal dose of such NPs. Our results demonstrate that Bi-based materials represent a critical tool against multidrug resistant bacteria and require greater attention within the community. We anticipate this study to inspire broader investigation into the use of other metal oxides as antimicrobial materials, particularly those that limit the development of resistant phenotypes.