Breakthrough Discovery Reveals Secret Antibacterial Factor in Manuka Honey

New research on Manuka Honey from New Zealand has unveiled another reason for its antibacterial activity.

Findings of a research laboratory in Singapore shows that a special molecule in Manuka honey acts to augment the antibacterial activity of methylglyoxal in the honey – a process known as synergy. The unique type of antibacterial activity in Manuka honey was originally discovered at the University of Waikato in New Zealand during the 1980s. Evidence shows Manuka honey's special antibacterial properties are effective at healing wounds and other skin conditions. Research also shows that this activity is only present in some Manuka honey.

Research indicates that methylglyoxal is responsible for the antibacterial activity in Manuka honey. However, researchers also feel there is another synergistic factor contributing to its antibacterial properties. Research has proven the existence of a special molecule that combines with the methylglyoxal molecule and other fractions in Manuka honey to create the powerful antibacterial activity that it is known for. This discovery is also the key to understanding why the clinically proven antibacterial activity is so effective and why research to date has shown that bacteria fail to develop the resistance that is inevitable with conventional antibiotics.

Research is now underway to confirm the mode of action of the synergist and to further understand its interaction with other fractions, including methylglyoxal. This latest research will provide the medical industry with a full scientific understanding of the antibacterial properties of Manuka honey.

The Manuka honey industry is now worth in excess of $100 million in export earnings. However, not all Manuka honeys are equal and the way to test potency has been an issue for some time. The original testing standard uses a simple method of comparing the bacterial kill-zone of a honey sample to the kill-zone of a standard antiseptic. For a variety of reasons this can't be perfect and is open to interpretation and a margin of error. The ideal objective is to have a simple analytical chemical test that can be carried out by any lab anywhere in the world. But such a test isn't possible until we know what we're trying to measure. Discovering the synergist was the key. Analysis now includes developing an algorithm to find the strength of a honey's antibacterial activity by measuring the level of the synergist and the level of methylglyoxal present. It will then be possible to very precisely determine the non-peroxide activity of Manuka honey.

Methylglyoxal in Manuka Honey – Correlation with Antibacterial Properties

Abstract

A perfect linear correlation was found for methylglyoxal levels in 61 samples of Manuka honey, ranging from 189 to 835 mg/kg, and the corresponding antibacterial activities of the samples, which were between 12.4% and 30.9% equivalent phenol concentration. This clearly underlines that methylglyoxal is the dominant bioactive compound in Manuka honey and above concentrations of around 150 mg/kg directly responsible for the characteristic antibacterial properties of Manuka honey. Methylglyoxal can be a suitable tool for labeling the unique bioactivity of Manuka honey.

Introduction

Manuka honey, derived from the Manuka tree (Leptospermum scoparium) in New Zealand, is well-known for a pronounced antibacterial activity which cannot be found in any other honey. Manuka honey has been reported to exhibit antimicrobial activity against pathogenic bacteria such as Staphylococcus aureus and Helicobacter pylori, making this honey to a promising functional food for the treatment of wounds, stomach ulcers, etc. Besides hydrogen peroxide, which is produced in most conventional honeys by the endogenous enzyme glucoseoxidase, several other non-peroxide factors were discussed to be responsible for the unique antibacterial activity of Manuka honey.

The Unique Manuka Factor (UMF) was introduced years ago, leading to a classification of premium products based on microbiological assays. A UMF of 10, for instance, has the same antibacterial activity to a 10% solution of phenol. Recently, researchers were able to demonstrate that the surprisingly high amounts of the 1,2-dicarbonyl compound methylglyoxal are present in Manuka honey. Methylglyoxal, at the levels at which were found it in Manuka honey, proved to be another non-peroxide antibacterial constituent. This observation was confirmed by scientists. The purpose of the present study was to investigate to which extent methylglyoxal is responsible for the non-peroxide antibacterial activity of Manuka honey, in order to check whether it is possible to back-reference from the methylglyoxal content to the antibacterial properties of a honey sample.

Materials and Methods

The source of the 61 samples of Manuka honey from New Zealand came from drums of honey selected on a spread of non-peroxide contents and of varying ages. The amount of methylglyoxal was measured as the corresponding quinoxaline after pre-column derivatisation with o-phenylendiamine using RP-HPLC with UV detection. The data for non-peroxide antibacterial activity were analyzed by a specially appointed laboratory for testing for antibacterial activity using criteria laid down by the Honey Research Unit at Waikato University, New Zealand. Antibacterial activity was expressed as equivalent phenol concentration (% w/v). This value is used commercially as the Unique Manuka Factor (UMF).

Results and Discussion

Methylglyoxal levels in 61 samples of Manuka honey ranged from 189 to 835 mg/kg honey. Corresponding antibacterial activities were between 12.4 and 30.9% equivalent phenol concentration. A good linear correlation (y = 8.388 + 0.0263x; r2 = 0.905) between methylglyoxal and the antibacterial activity was found. This indicates that methylglyoxal is directly responsible for the characteristic antibacterial properties of Manuka honey. Our data is in perfect agreement with results published by Adams who had reported data for 49 samples of Manuka honey. In their study, concentrations of methylglyoxal as measured according to Mavric ranged from 25 to 709 mg/kg.

Corresponding antibacterial activity was between “not detectable” and 27.5% equivalent phenol concentration. Among the samples analyzed by Adams, 30 samples had antibacterial activities higher or equal 10% equivalent phenol concentration. Plotting these 30 samples together with data obtained in our study, a perfect match of the data sets can be obtained. This remarkable agreement of results obtained in two independent studies clearly underlines the final statement that methylglyoxal is the dominant bioactive compound in Manuka honey and starting from concentrations of approximately 150 mg/kg is exclusively responsible for the pronounced antibacterial activity. Due to limited sensitivity and inaccuracy of the used test system, data obtained for antibacterial activities below 10% equivalent phenol concentration must be handled with care. This may explain the fact that the corresponding regression lines in Figure 1 do not pass through the origin (parameter a = 8.388 or 7.783, respectively). Furthermore, for such low antibacterial activities, other factors such as polyphenols, organic acids or currently unknown compounds may additionally contribute to non-peroxide antibacterial properties.

In conclusion, methylglyoxal is a unique antibacterial compound found in high concentrations in Manuka honeys from New Zealand and directly responsible for the specific antibacterial activity of these samples. Methylglyoxal can serve as a suitable tool for the labeling of the bioactivity of commercial products.



Figure 1. (A) correlation between methylglyoxal and antibacterial activity for 61 samples of Manuka honey analyzed in this study, (B) data analyzed in this study plus data from Allen shown as filled triangles

How Manuka Honey Fights Infection

Scientists at the University of Wales Institute, Cardiff, have uncovered that Manuka honey can help fight infection by destroying key bacterial proteins.

Led by Dr. Rowena Jenkins, the research team investigated the mechanisms of Manuka honey action. They found that its antibacterial properties were not due solely to the sugars present in the honey. They grew Meticillin resistant Staphylococcus aureus (MRSA) in the laboratory and treated it with and without Manuka honey for four hours. The experiment was repeated with sugar syrup to determine whether the effects were due to sugar content in honey alone.

The bacterial cells were then broken and the proteins isolated and separated on a system that displayed each protein as an individual spot. The researchers saw many fewer proteins from the Manuka honey-treated MRSA cells, and one particular protein called FabI seemed to be completely missing.

FabI is a protein that is needed for fatty acid biosynthesis. This essential process supplies the bacteria with precursors for important cellular components such as lipopolysaccarides and its cell wall.

The scientists said that the absence of those proteins in honey-treated cells could help explain the mode of action of Manuka honey in killing MRSA.

Manuka and other honeys have been known to have wound healing and anti-bacterial properties for some time. However, the way in which they act is still not known. If scientists can discover exactly how Manuka honey inhibits MRSA, it could be used more frequently as a first-line treatment for infections with bacteria that are resistant to many currently available antibiotics.

The work was presented at the Society for General Microbiology’s meeting at Heriot-Watt University, Edinburgh.