New research suggests that (some of) the secrets to honey’s anti-bacterial properties may have been revealed.
A Dutch team of microbiologists propose that the anti-bacterial properties of the honey they tested come down to four chemicals and one general property:
Sugars High concentrations of sugars have long been known to have anti-bacterial properties and are used in preserving food.
The best known effect is by soaking up water. Bacteria, like most living things, need water. Soak up the water and they’ll dehydrate.
Ever tried to clean up a wine spill in the carpet by dribbling some water over the stain, then sprinkling salt over the water? You’ll know how the salt sucks up the water from the carpet.
In a similar way, high concentrations of sugar outside cells, can suck water out of the cells or absorb other moisture that’s around. This works through creating an osmotic gradient, where the moveable part – water – moves to balance the low concentration of water outside the cell, dehydrating the cell.
H2O2 Hydrogen peroxide is a bleach used in making paper among other things. Household bleach kills bacteria, so does hydrogen peroxide.
Methylglyoxal (MGO) This is known to be cytotoxic (kills cells). There is evidence that this is created from dihydroxyacetone in manuka honey stored at warm temperatures. Something similar might be happening in the honey the Dutch scientists tested.
Defensin-1 One of several anti-bacterial peptides (small protein) found in bees, defensin-1 is part of the bee’s defence against bacterial infection. It’s also found in royal jelly, what queen bees are fed by their worker bees. (Royal jelly also has an epigenetic effect: it causes the larvae to become a queen bee, rather than a worker bee.) A wider range of anti-bacterial peptides are present in Asian honeybees than found in the domesticated Western honeybee; it would be interesting to know if honey from different types of bees have different anti-bacterial peptides.
Acidity The acidity of honey had a small effect too. Honey is acidic, neutralising this to neutral pH (not acidic or alkaline) removed this effect.
None of the individual compounds identified are new and their anti-bacterial actions are already known.
What is news is that these are the particular compounds giving the honey tested it’s anti-bacterial properties and seem to account for all the anti-bacterial properties against the bacteria tested.
Rather than extracting compounds from the original honey, they neutralised each candidate compound in turn, noting the loss of anti-bacterial properties.
By varying the neutralisations applied, they could work out which combination of compounds was effective in killing which bacteria.
Different combinations had different effects on different bacteria. Some factors had overlapping contributions, requiring the presence of one of the other factors for full effect. The overall combination was effective against all the bacteria tested, giving a broad spectrum antibiotic effect against the bacteria tested.
Several of the bacteria tested had known antibiotic resistance.
Kwakman, P., te Velde, A., de Boer, L., Speijer, D., Vandenbroucke-Grauls, C., & Zaat, S. (2010). How honey kills bacteria The FASEB Journal, 24 (7), 2576-2582 DOI: 10.1096/fj.09-150789
Xu, P., Shi, M., & Chen, X. (2009). Antimicrobial Peptide Evolution in the Asiatic Honey Bee Apis cerana PLoS ONE, 4 (1) DOI: 10.1371/journal.pone.0004239
Adams, C., Manley-Harris, M., & Molan, P. (2009). The origin of methylglyoxal in New Zealand manuka (Leptospermum scoparium) honey Carbohydrate Research, 344 (8), 1050-1053 DOI: 10.1016/j.carres.2009.03.020
Press release (via EurekaAlert)
For a soft introduction to bees, this gives an overview suitable for kids. (Or those who are lazy! – it’s short and well-written.)
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