Releasable antimicrobial polymer-silk coatings for combating multidrug-resistant bacteria

Abstract

The development of new and effective wound dressing materials is still in demand especially considering the growing incidence of infections caused by multidrug-resistant (MDR) bacteria. In this study, we report the facile fabrication of robust silk films with embedded synthetic cationic antimicrobial polymers that can be released to combat planktonic bacteria and inhibit biofilm formation on the substrate surface. The coatings can be primed on glass or cotton substrates. The release profile of the antimicrobial polymer is tunable based on the polymer concentration, silk to polymer ratio, and film configuration. Exposure of the antimicrobial polymer-silk coating to planktonic bacteria (ca. 10⁸ colony forming units (CFU) mL⁻¹) over 6.5 h (and up to 24 h) yielded 5 to 7 log₁₀ reduction in bacterial viability and ca. 7 log₁₀ inhibition of biofilm formation against Pseudomonas aeruginosa, including a MDR strain. Against a methicillin and MDR Staphylococcus aureus strain, ca. 5 log₁₀ reduction in bacterial viability and 3 log₁₀ reduction in the biofilm growth were achieved. The efficacy and the simplicity of the coating methodology thus suggest that the antimicrobial polymer-silk films can potentially be applied as wound dressing materials as well as coatings for biomedical implants to combat bacterial infections.