Compositional analysis of Scottish honeys with antimicrobial activity against antibiotic-resistant bacteria reveals novel antimicrobial components

•Scottish honeys had antimicrobial activity against antibiotic-resistant bacterial isolates.•Some Scottish honeys were as effective as the known antimicrobial Manuka Medihoney®.•Inhibition was not correlated with pH, sugar, phenol content or antioxidant capacity.•LC-MS identified potential active components including novel fatty diacid glycosides.

Antibiotic-resistant bacteria are a major health concern and honey may provide an alternative to antibiotic use under certain conditions. The antimicrobial action of six Scottish honeys and Manuka Medihoney® was compared against antibiotic-resistant Acinetobacter calcoaceticus, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli. Certain Scottish honeys, such as Highland and Portobello honey 2011, were comparable in effectiveness to the established antimicrobial Medihoney®, inhibiting growth to <1 compared to 10 log10 CFU/ml in the control. Heather honey was the next most active while Blossom honeys were less active. Bacteria were inhibited by a sugar-matched control, but to a lesser extent, indicating that antimicrobial activity was associated with non-sugar components, such as polyphenols. However, total phenol content or antioxidant capacity did not correlate with antimicrobial activity. Liquid chromatography-mass spectrometric analysis revealed that the composition of polyphenol and non-polyphenol components differed between honeys. In addition, candidate components that could be associated with antimicrobial activity were noted including novel fatty diacid glycoside derivatives not previously identified in honeys.