The intracellular effects of manuka honey on Staphylococcus aureus

The purpose of this study was to investigate the effect of manuka honey on Staphylococcus aureus in order to identify the intracellular target site. The mode of inhibition of manuka honey against S. aureus NCTC 10017 was investigated by determining the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC) and the effect of time on viability. Structural changes were observed by scanning (SEM) and transmission electron microscopy (TEM) of cells suspended for 4 h at 37°C in 0.05 mM Tris buffer containing 10% (w/v) manuka honey and were compared to cells in buffer alone or buffer containing 10% (w/v) artificial honey (to assess osmotic damage). A bactericidal mode of inhibition for manuka honey on S. aureus was established. Marked structural changes in honey-treated cells were seen only with TEM, where a statistically significant increase in the number of whole cells with completed septa compared to untreated cells were observed (P < 0.05). Structural changes found with TEM suggest that honey-treated cells had failed to progress normally through the cell cycle and accumulated with fully formed septa at the point of cell division without separating. Sugars were not implicated in this effect. The staphylococcal target site of manuka honey involves the cell division machinery.