Novel nano-composite hydrogels with honey effective against multi-resistant clinical strains of Acinetobacter baumannii and Pseudomonas aeruginosa.

Novel alginate hydrogels with silver nanoparticles (AgNPs) and honey components were produced with the aim to target multidrug-resistant bacterial strains causing nosocomial wound infections. AgNP synthesis was optimized in highly concentrated honey solutions so that a 5-month stable, colloid solution with 50% of honey and ~ 8 nm AgNPs at neutral pH was obtained. The colloid solution was further used to produce nano-composite Ag/alginate hydrogels in different forms (microbeads, microfibers and discs) that retained all AgNPs and high fractions of honey components (40-60%) as determined by the phenol-sulfuric acid and Folin-Ciocalteu methods. The hydrogels were characterized by UV-Vis spectroscopy and Fourier-transform infrared-attenuated total reflectance spectroscopy while the antibacterial activity was investigated against a broad spectrum of Gram-negative and Gram-positive bacteria, including 13 multi-resistant clinical strains of Acinetobacter baumannii, one clinical strain of Pseudomonas aeruginosa and one clinical strain of Staphylococcus aureus. At the total released silver concentration of ~ 9 μg/ml, the hydrogels exhibited strong bactericidal activity against standard and most of the investigated multi-resistant hospital strains with the exemption of 3 clinical strains of A. baumannii in which antibacterial effects were absent. These results reveal the need for further in-depth studies of bacterial resistance mechanisms and, in the same time, potentials of the novel Ag/alginate hydrogels with honey components to combat wound infections and enhance healing as non-sticky, antibacterial, and bioactive dressings.