Anti-biofilm properties of Portuguese honeys against multi-drug resistant microorganisms: A promising strategy for chronic wounds healing

Honey is considered a promising strategy for chronic wound management, being a possible solution for bacterial resistance problem mostly due to its physical-chemical features. However, these properties might vary significantly depending on the honey floral source. Dark-colored honey, such as chestnut honey, is related to increased antioxidant and bactericidal properties. This study aims to assess biofilms of multidrug-resistant microorganisms in honey samples from the Natural Park of Montesinho, in Portugal, which is considered a region with predominant chestnut floral source. The minimum inhibition concentration (MIC) of honey was tested for Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Candida albicans. The biofilm removal as well as the metabolic inactivation of the biofilms were evaluated using three honey concentrations: 1xMIC, 5xMIC, and 10xMIC. The biofilm viability was analyzed with fluorescent microscopy. Honey samples were characterized according to the pollen profile, phenolic composition, H2O2 levels, tyrosinase inhibition, and pH. The antioxidant capacity was determined through FRAP and ABTS assays. Most of the honey samples exhibited a MIC of 6.75%. Biofilm removal efficacy differs among samples. Regression analysis evidenced a positive correlation between the biofilm removal and concentrations of H2O2, vanillic acid, pinocembrin, Cytisus striatus and Corrigiola telephiifolia, and pH. The honey concentration of 10xMIC was the most effective to inhibit the biofilm metabolism and viability. The concentrations of C. sativa, H2O2, and the anti-tyrosinase and FRAP activities were also positively correlated. The honey samples had a dominant presence of Castanea sativa pollen and were effective against biofilms formed by multidrug-resistant microorganisms.