The antimicrobial mechanism of Greek thyme honeys against methicillin-resistant Staphylococcus aureus clinical isolates: a case study of comparison with Manuka honey

The antibacterial potential of honey has been of great scientific interest. Understanding the underlying mechanism is essential to explore its potential as therapeutic alternative against a range of (non)pathogenic microorganisms. The floral origin of honey is critical for its antibacterial activity and Greek thyme honeys have been of increasing interest due to their chemical composition and bioactivity. In this study, the antimicrobial effect of six Greek honeys, with different percentages of thyme pollen grains and two Manuka honeys were tested against four MRSA clinical isolates (ATCC 43300, 0791, 28965, 01322). Agar-well diffusion assay and total viable counts were used to examine the antimicrobial strength of honeys, while the effect thereof on cellular redox state and cell membrane was tested by flow cytometry. Thyme honeys had superior or equal antimicrobial strength compared to this of Manuka, while thermal processing did not significantly affect this activity. Acidity and the high H2O2 content, common features for all thyme honeys, caused cellular oxidative damage and cell death unlike observed in Manuka-treated populations. The activity of the monofloral thyme honey (74% thyme pollen) was higher than the other indigenous polyfloral samples, which confirms the medicinal importance of this medicinal plant.