The Antibacterial Activity of Australian <i>Leptospermum</i> Honey Correlates with Methylglyoxal Levels

<div><p>Most commercially available therapeutic honey is derived from flowering <i>Leptospermum scoparium</i> (manuka) plants from New Zealand. Australia has more than 80 <i>Leptospermum</i> species, and limited research to date has found at least some produce honey with high non-peroxide antibacterial activity (NPA) similar to New Zealand manuka, suggesting Australia may have a ready supply of medical-grade honey. The activity of manuka honey is largely due to the presence of methylglyoxal (MGO), which is produced non-enzymatically from dihydroxyacetone (DHA) present in manuka nectar. The aims of the current study were to chemically quantify the compounds contributing to antibacterial activity in a collection of Australian <i>Leptospermum</i> honeys, to assess the relationship between MGO and NPA in these samples, and to determine whether NPA changes during honey storage. Eighty different <i>Leptospermum</i> honey samples were analysed, and therapeutically useful NPA was seen in samples derived from species including <i>L</i>. <i>liversidgei</i> and <i>L</i>. <i>polygalifolium</i>. Exceptionally high levels of up to 1100 mg/kg MGO were present in <i>L</i>. <i>polygalifolium</i> honey samples sourced from the Northern Rivers region in NSW and Byfield, QLD, with considerable diversity among samples. There was a strong positive relationship between NPA and MGO concentration, and DHA was present in all of the active honey samples, indicating a potential for ongoing conversion to MGO. NPA was stable, with most samples showing little change following seven years of storage in the dark at 4°C. This study demonstrates the potential for Australian <i>Leptospermum</i> honey as a wound care product, and argues for an extension of this analysis to other <i>Leptospermum</i> species.</p>