Manuka honey is made using manuka flower nectar

The potential medical benefits of manuka honey have been in the news today, with several newspapers reporting on honey’s ability to inhibit various types of bacteria, including antibiotic-resistant “superbugs”, such as MRSA.

Honey has long been known to have antibacterial properties and is sometimes included in licensed wound-care products. However, researchers discussing its use at a scientific conference have said it is not widely used because the way it works is not understood. They have presented research that demonstrates how manuka honey can stop bacteria from attaching to tissue at the molecular level. They have also presented a study that indicates that combining honey with certain antibiotics may make them more successful against drug-resistant MRSA.

The laboratory research behind these claims is of particular interest as it also highlights the growing concern about the spread of drug-resistant bacteria, which was last week highlighted by a new report from the World Health Organization. However, the effectiveness of honey in combination with antibiotics has yet to be tested in clinical trials and further research is still needed to assess whether it could be used to treat drug-resistant infections.

It is important to note that the honey used in the trials was filtered, medical-grade honey with all impurities removed. People should not try using honey bought from supermarkets to treat wounds at home.

What is manuka honey?

Manuka honey comes from nectar collected by honeybees foraging on the manuka tree, which grows in New Zealand. Honey of all kinds has been used in traditional remedies for thousands of years, both for clearing wound infections and to enhance healing of chronic wounds. This type of honey, in purified form, is already used in licensed wound-care products, and is considered to be a viable alternative to topical treatments for surface wound infections. However, the researchers point out there is some reluctance to use these products because the way honey works to fight infection (its mechanism of action) is not known.

The researchers also say that honey has been shown to exhibit “broad-spectrum” antimicrobial activity, being able to act upon more than 80 species of pathogen. They point towards previous research that has demonstrated that honey can inhibit pathogens normally capable of causing wound infection, including strains that are resistant to conventional antibiotics. They also highlight the growing number of clinical reports that have shown that wound infections (including those infected with MRSA) can be cleared by the topical application of manuka honey.

How is it meant to work?

The researchers point out that honey is a complex and variable product, so searching for “specific inhibitors” (the molecular compounds that might have an effect on bacteria) has not been easy. They think that several factors may together be implicated in its antimicrobial activity, including its high sugar content, low water content, low acidity, the presence of hydrogen peroxide and the presence of phytochemicals.

Manuka honey is thought to be particularly potent because it has high levels of a compound called dihydroxyacetone, which is present in the nectar of manuka flowers. This chemical produces methylglyoxal, a compound thought to have antibacterial and cell-killing properties.

What did the new research involve?

The new research involved laboratory studies looking at how manuka honey affects the molecular structure of three bacteria. They were:

• Staphylococcus aureus (MRSA-15), which is a common cause of wound infection and has become resistant to antibiotics. In this study, researchers looked at different concentrations of honey in order to determine the lowest concentration needed to induce antimicrobial activity. Researchers also tested several antibiotics for antibacterial activity, both alone and when combined with honey.
• Pseudomonas aeruginosa, which is a multi-drug resistant bacteria that causes persistent infections in burns patients and chronic venous leg ulcers. In this study, the bacteria were exposed to different “sub-lethal” concentrations of manuka honey for three hours to determine the concentration at which the bugs were inhibited. The cell proteins were then compared to untreated cells using specialised methods.
• Streptococcus pyogenes (Group A streptococci), which causes numerous infections, both superficial and life-threatening. The researchers looked at whether different concentrations of honey could inhibit the growth of bacterial biofilm (which allows bacterial cells to adhere to each other).

What has the new research found?

Overall, the researchers found that manuka honey affected the structure and activity of different bacteria.

• In the study of MRSA, the bacteria were susceptible to “relatively low” concentrations of manuka honey. Combining honey with the antibiotic oxacillin (and to a small extent vancomycin) altered the structure of these drugs, making them potentially more effective. This was measured as the minimum inhibitory concentration or minimum bactericidal concentrations, which are each a measure of the concentration of drug needed to slow growth or kill the organisms.
• In the study of Pseudomonas bacteria, the honey induced “significant changes” in the bacteria’s protein expression, which is likely to be detrimental to its survival.
• In the study of Streptococcus pyogenes, honey inhibited the growth of bacterial biofilms.

What were the researchers’ conclusions?

Professor Rose Cooper from the University of Wales Institute Cardiff, who was one of the researchers, explained that the findings with Streptococci and Pseudomonas “suggest that manuka honey can hamper the attachment of bacteria to tissues”, an essential step in the initiation of acute infections.

Inhibiting attachment also blocks the formation of biofilms, which can protect bacteria from antibiotics and allow them to cause persistent infections, she explained. “Other work in our lab has shown that honey can make MRSA more sensitive to antibiotics such as oxacillin – effectively reversing antibiotic resistance. This indicates that existing antibiotics may be more effective against drug-resistant infections if used in combination with manuka honey.”

The research may increase the clinical use of manuka honey as doctors are faced with the threat of “diminishingly effective” antimicrobial options, she argues. “The use of a topical agent to eradicate bacteria from wounds is potentially cheaper and may well improve antibiotic therapy in the future. This will help reduce the transmission of antibiotic-resistant bacteria from colonised wounds to susceptible patients”, she adds.