Finding out how honey kills bacteria

Honey has been renowned for its wound healing properties since ancient times, but only in recent years has an evidence base developed for its use in modern medicine.

As “Didapper” has mentioned (PJ, 16 January 2010, p61), a Cochrane review in 2008 found that honey was more effective in reducing healing time than some gauze and film dressings that are often used to treat moderate burns. However, the researchers were unable to show any clear benefits for the healing of grazes, lacerations, surgical wounds and leg ulcers.

How honey heals wounds has never been clear. It may help the body remove dead tissue and provide a good environment for tissue regrowth. But at least part of its influence is believed to lie in its antibacterial properties.

Given the widespread antibiotic resistance and slow progress towards new antibiotics, the possibility of finding new antibacterial strategies is attractive. Researchers have therefore been looking not only at honey’s mechanism of action but also at applying its antibacterial factors in medicine.

Honey has shown potent in vitro activity against antibiotic-resistant bacteria but, until new research emerged from the Netherlands in 2010, its only well characterised antibacterial factors were known to be hydrogen peroxide and, specifically in manuka honey, methylglyoxal. Its high osmolarity derived from its sugar content also has an antibacterial effect.

The Dutch researchers found a hitherto unidentified compound, bee-defensin-1, a protein made by bees which they add to the honey.

This finding emerged from a study in which a specially prepared medical grade honey was evaluated against a panel of antibiotic-resistant, disease-causing bacteria, including Bacillus subtilis, meticillin-resistant Staphylococcus aureus, extended spectrum ß-lactamase Escherichia coli, ciprofloxacin-resistant Pseudomonas aeruginosa and vancomycin-resistant Enterococcus faecium.

The researchers developed a method selectively to neutralise the known antibacterial factors in honey — ie, hydrogen peroxide and methylglyoxal — and determine their individual antibacterial contributions. After combined neutralisation of these factors, honey retained significant antibacterial activity.

Further work led to the isolation of the defensin-1 protein, which is part of the honey bee immune system. After analysis, the scientists concluded that the antibacterial properties come substantially from defensin-1 rather than the other antibacterial ingredients.

These findings could be of value in developing more effective antibacterials for treating infection as well as contributing to knowledge about the usefulness of honey in wound healing. Moreover, such medically characterised honeys could serve as novel agents to prevent or treat infections, in particular those caused by antibiotic-resistant bacteria.

The study has also shed light on the inner workings of honey bee immune systems, which, the researchers say, may one day help breeders create healthier and heartier honey bees.