Targeting biofilms of multidrug-resistant bacteria with silver oxynitrate

A topical antimicrobial, silver oxynitrate (Ag₇NO₁₁), has recently become available that exploits the antimicrobial activity of ionic silver but has enhanced activity because highly oxidised silver atoms are stabilised with oxygen in a unique chemical formulation. The objective of this study was to use a multifaceted approach to characterise the spectrum of antimicrobial and antibiofilm activity of a wound dressing coated with Ag₇NO₁₁ at a concentration of 0.4 mg Ag/cm². Physiochemical properties that influence efficacy were also evaluated, and Ag₇NO₁₁ was found to release a high level of Ag ions, including Ag²⁺ and Ag³⁺, without influencing the pH of the medium. Time-kill analysis demonstrated that a panel of multidrug-resistant pathogens isolated from wound specimens remained susceptible to Ag₇NO₁₁ over a period of 7 days, even with repeated inoculations of 1 × 10⁶ CFU/mL to the dressing. Furthermore, established 72-h-old biofilms of Pseudomonas aeruginosa, Staphylococcus aureus and two carbapenem-resistant Gram-negative bacteria (bla_NDM-1-positive Klebsiella pneumoniae and bla_VIM-2-positive P. aeruginosa) were disrupted and eradicated by Ag₇NO₁₁ in vitro. Ag₇NO₁₁ is a proprietary compound that exploits novel Ag chemistry and can be considered a new class of topical antimicrobial agent. Biocompatibility testing has concluded Ag₇NO₁₁ to be non-toxic for cytotoxicity, acute systemic toxicity, irritation and sensitisation.