Medicinal Manuka

Manuka honey has received considerable attention recently due to its impressive antimicrobial ability and potential for future clinical use.

Manuka honey is produced by European honeybees (Apis mellifera) that visit the Manuka tree (Leptospermum scoparium) in New Zealand. It is most commonly distributed as monofloral honey (produced by bees that have visited predominantly one plant species—in this case, the Manuka bush); however, it can also be sold as multifloral.

The Manuka tree, which the European honeybees visit, has a long history of use for its medicinal properties. The Māori (the indigenous Polynesian people of mainland New Zealand) valued it for its wide variety of uses, referring to the plant as ‘taonga’ (‘treasure’). The leaves from the tree were used to make infusions that could reduce fevers, and the gum produced from the tree was used to moisturise burns and soothe coughs. In the 18th century, European settlers contacted the Māori and became aware of this tree and its healing properties; they used the leaves as a medicinal tea to treat scurvy. 

In 1839, an English beekeeper, Mary Bumby, introduced bees to New Zealand, and by 1860, the bee population had grown extensively, and colonies were present throughout forests. The Māori learnt to harvest the honey produced by these bees and promoted the production of Manuka honey. The honey was used by the Māori for the same benefits they used the Manuka tree. In the 1980s, the biochemist Peter Molan launched the first scientific research on the antimicrobial properties of Manuka honey, evaluating its ability to kill microbes.

Research has demonstrated that Manuka honey is an effective bactericidal (killer of microbes). Dr Jonathon Cox and his colleagues at Aston University showed that administering Manuka honey can be effective against Mycobacterium abscessus, which is fatal without treatment. Using a model of an artificial lung, Dr Cox found that the addition of Manuka honey reduced the dosage of the highly potent amikacin by 8-fold, which is an extremely significant difference to the quality of life of patients as a common consequence of the 13-month amikacin treatment is permanent hearing loss. 

Alternative remedies for bacterial infections are required to combat the growing concern of antibiotic resistance. Many molecules of Manuka honey are responsible for their antimicrobial activity, including methylglyoxal (MGO) content. MGO can interfere with the lipid bilayer structure of the bacterial membrane, leading to leakage of its cellular contents and cell death. MGO can also impair the function of enzymes involved in energy production and macromolecule synthesis within bacteria. Additionally, Manuka honey can also produce hydrogen peroxide, which generates highly reactive oxygen species (ROS) within bacterial cells. These ROS, such as hydroxyl radicals, can cause oxidative damage to biomolecules, including proteins, lipids, and DNA, leading to bacterial cellular death. Altogether, these mechanisms enable Manuka honey to disrupt bacterial growth and proliferation. 

Manuka honey is currently used as a medical product for professional wound care in European hospitals. The main advantage of Manuka honey is that the mechanisms behind its antibacterial activity are diverse, making it effective against resistant strains of bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). A systematic review written by Jonathon Cox states that certain commercially available varieties of Manuka honey are effective against organisms that have a high degree of antibiotic resistance. Therefore, this leads to the promising preliminary conclusion that Manuka honey could be the answer to the investigation of finding an effective antimicrobial, an alternative to antibiotics.

Written by Harvey Wilkes  

Related article: Natural substances as treatment to infection

REFERENCES

Nolan, V.C., Harrison, J. and Cox, J.A., 2022. In vitro synergy between manuka honey and amikacin against Mycobacterium abscessus complex shows potential for nebulisation therapy. Microbiology, 168(9), p.001237.

Nolan, V.C., Harrison, J., Wright, J.E. and Cox, J.A., 2020. Clinical significance of manuka and medical-grade honey for antibiotic-resistant infections: a systematic review. Antibiotics, 9(11), p.766.