Beschreibung:
<jats:p>The emergence of multidrug resistant bacteria, especially biofilm‐associated <jats:italic>Staphylococci</jats:italic>, urgently requires novel antimicrobial agents. The antibacterial activity of ultrasmall gold nanoparticles (AuNPs) is tested against two gram positive: <jats:italic>S. aureus</jats:italic> and <jats:italic>S. epidermidis</jats:italic> and two gram negative: <jats:italic>Escherichia coli</jats:italic> and <jats:italic>Pseudomonas aeruginosa</jats:italic> strains. Ultrasmall AuNPs with core diameters of 0.8 and 1.4 nm and a triphenylphosphine‐monosulfonate shell (Au0.8MS and Au1.4MS) both have minimum inhibitory concentration (MIC) and minimum bactericidal concentration of 25 × 10<jats:sup>−6</jats:sup><jats:sc>m</jats:sc> [Au]. Disc agar diffusion test demonstrates greater bactericidal activity of the Au0.8MS nanoparticles over Au1.4MS. In contrast, thiol‐stabilized AuNPs with a diameter of 1.9 nm (AuroVist) cause no significant toxicity in any of the bacterial strains. Ultrasmall AuNPs cause a near 5 log bacterial growth reduction in the first 5 h of exposure, and incomplete recovery after 21 h. Bacteria show marked membrane blebbing and lysis in biofilm‐associated bacteria treated with ultrasmall AuNP. Importantly, a twofold MIC dosage of Au0.8MS and Au1.4MS each cause around 80%–90% reduction in the viability of <jats:italic>Staphylococci</jats:italic> enveloped in biofilms. Altogether, this study demonstrates potential therapeutic activity of ultrasmall AuNPs as an effective treatment option against staphylococcal infections.</jats:p>