Study of the Anti-Staphylococcal Potential of Honeys Produced in Northern Poland

Abstract

The antimicrobial activity of 144 samples of honeys including 95 products from apiaries located in Northern Poland was evaluated. The antibacterial activity of those natural products, their thermal stability, and activity in the presence of catalase was investigated by microdilution assays in titration plates. The MTT assay was performed for the determination of anti-biofilm activity. Spectrophotometric assays were used for the determination of antioxidant potential, total phenolic content, and ability to generate hydrogen peroxide. Some of the investigated honeys exhibited surprisingly high antimicrobial, especially anti-staphylococcal, potential, with Minimal Inhibitory Concentration (MIC) values of only 1.56% (v/v). Much higher resistance was observed in the case of staphylococci growing as biofilms. Lower concentrations of the product, up to 12.5% (v/v) stimulated its growth and effective eradication of biofilm required concentration of at least 25% (v/v). Hydrogen peroxide has been identified as a crucial contributor to the antimicrobial activity of honeys supplied by Polish beekeepers. However, some of the results suggest that phytochemicals, especially polyphenols, play an important role depending on botanical source (both positive, e.g., in the case of buckwheat honeys as well as negative, e.g., in the case of some rapeseed honeys) in their antimicrobial potential.

Keywords: MIC; Staphylococcus; antibacterial activity; antioxidants; biofilm; correlations; honey; phenolics.

Figure 1

Time-kill curves of S. aureus ATCC 25923 cultivated in absence or presence of two the most active honeys: (a) multi-floral honey and (b) buckwheat honey, both collected by professional beekeepers; in comparison to manuka honey (c). Concentrations of honeys are presented in relation to MBC determined.

Figure 2

Anti-biofilm activity of selected honeys: (a) 86; (b) 35; (c) manuka.

Figure 3

Results of statistical analyses of correlation between antimicrobial activity and some of the investigated parameters: (a) total phenolic content; (b) antioxidative properties determined with DPPH assay; (c) antioxidative properties determined with FRAP assay; (d) concentration of generated hydrogen peroxide; (e) acidity—pH value.

Figure 4

Investigation of hydrogen peroxide concentrations in honey solutions prepared in 100 μM H₂O₂ as a solvent; (a,b) lime tree (c,d) multi-floral (e,f) buckwheat (g,h) rape honey.