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Honey wound healing chemically complex

14 May, 2013

New research into the infection-fighting properties of New Zealand’s Mānuka honey has shown that, though the compound methylglyoxal (MGO) plays a role in inhibiting bacteria, it is not the full story.

Higher levels of MGO in Mānuka honey

Previous research has shown that Mānuka honey can effectively treat chronic wound infections (wounds that are slow to heal). All honeys have some antibacterial properties and have been used since ancient times in wound treatment. However, Mānuka honey has been found to be more effective when compared with other honeys. As the honey has higher levels of MGO than other honeys, this bacteria-inhibiting substance is widely credited as being the reason for the honey’s effectiveness.

However, the researchers found that, even when MGO was chemically removed, the honey still retained antibacterial properties, suggesting that the honey’s role in inhibiting bacteria growth is more chemically complex than previously thought. In addition, it suggests that artificially increasing MGO levels in other honeys (as currently happens in some overseas honeys) to mimic Mānuka honey properties may be of limited value, although research on this would be needed.

Comparing Mānuka, Kānuka and clover honeys

The researchers examined Mānuka, Mānuka/Kānuka, Kānuka and clover honeys to determine which was the most effective at inhibiting the growth of four types of bacteria commonly found in chronic wounds. They also used Mānuka and Kānuka honeys from different locations around New Zealand to see if geography played a role in the honey’s effectiveness. The four different bacterial species were Baccilus subtilis, Pseudomonas aeruginosa, Escherichia coli (E. coli) and Staphylococcus aureus. Some strains of Staphylococcus aureus have already acquired resistance to some antibiotics.

In particular, the research team looked at two key honey ingredients known to inhibit bacterial growth – MGO and hydrogen peroxide, which is present in many honeys at varying concentrations, including Mānuka.

“Honey has long been known to have antibacterial activity. We wanted to compare the effectiveness of different honeys on various bacteria to determine how the different MGO and hydrogen peroxide levels in these honeys relate to bacterial growth inhibition,” says lead researcher Professor Liz Harry from the ithree Institute, University of Technology, Sydney, in a PLOS ONE media statement.

Chemical complexity of honey

“What we saw was that the Mānuka honeys were the most effective at inhibiting growth of all the bacteria. Interestingly, the MGO level alone cannot explain the variation in the effects we saw. The key to the effectiveness of honey is its chemical complexity – it contains several chemicals that inhibit bacterial growth, not just MGO. Unlike antibiotics, it is not expected that bacteria will become resistant to honey, a claim that has been supported by our research. Honey is an excellent example of where years of evolution can provide an effective long-term medical solution compared to the alternative of pure-compound antibiotics to which bacteria will always eventually develop resistance.”

In terms of effectiveness at slowing the rate at which the bacteria multiplied, Mānuka came in first, followed by the Mānuka/Kānuka mixture, then Kānuka and in last place the clover honey.

Role of hydrogen peroxide

As well as the MGO, the hydrogen peroxide certainly plays a role. When its properties were counteracted with a chemical called catalase, the honey’s antibacterial properties were reduced. However, some antibacterial properties still remained, even when MGO was also removed or at low levels, that could not solely be attributed to the remaining sugar content, suggesting the other chemicals are also playing a role in fighting the bacteria.

The researchers also found that the bacterial cells showed a varied and diverse set of responses to the different honeys. These responses included changes in cell length, cells bursting and changes to the way the bacteria’s DNA looked.

The research was published on 14 February 2013 in the open-access science journal PLOS ONE.

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