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by Craig Davis
Report prepared June 2002
Publsihed in October 2005
RIRDC Web Publication No W05/159 RIRDC Project No DAQ-232A
Executive Summary
The use of honey as a therapeutic
agent dates to ancient times. More recently, there has been growing interest
in this ‘natural’ remedy, which has lead to legitimate scientific investigations.
Research has shown that particular honeys have very special healing properties.
One group of honeys (Leptospermum honeys) have been described as
"the best natural antibiotic in the World".
Honeys have been shown to be active against a diverse range of microorganisms and reports of the inhibitory effect of honey on specific microorganisms are numerous. Honey has been shown to be effective against both Gram positive and Gram negative organisms, aerobic and anaerobic bacteria, as well as inhibiting spore germination of Bacillus cereus. The sensitivity of different bacterial species and strains to honey is extremely variable. Honey has also recently been shown to have an inhibitory effect against antibiotic resistant strains (e.g. golden Staph), which are frequently responsible for postoperative wound infection in immunologically compromised patients.
Much research effort has centred on establishing the properties of honey to which its antibacterial activity may be attributed. Such factors as osmolarity, acidity, hydrogen peroxide content and chemical components of honey have all been considered to contribute to the inhibition of bacterial growth. Honey is a highly saturated sugar solution which could suggest that this characteristic of honey would convey an antimicrobial effect. The high concentration of sugars leaves very little available water for the growth of microorganisms. However, the osmolarity of honey does not appear to be a major factor. The acidity of honey has also been suggested to explain the antibacterial activity of honey. Honey contains many organic acids, predominantly gluconic acid produced from glucose by glucose oxidase, and is characteristically acidic with pH 3.2 to 4.5. Although such an acidity level would be inhibitory to the growth of most bacterial species, there appears to be no correlation between antibacterial activity and the acidity of the honey. There is much evidence to suggest that the antibacterial activity of honey is due to more than the sugars present therein. Two major sources have been shown to be responsible for the anti-microbial activity - hydrogen peroxide (from the bee) and uncharacterised chemical substances (from the floral source). Hydrogen peroxide is known to have antimicrobial properties and can be removed efficiently by the addition of catalase to the honey prior to testing for antibacterial activity.
This project has investigated the correlation between antimicrobial activity and the non-peroxide activity of particular Leptospermum-derived honeys. Initial investigations tested the efficacy of these honeys against one particular bacteria (Staphylococcus aureus), while later studies assessed the effect of this honey on a range of food pathogens, animal pathogens (e.g. in mastitis) and human pathogens (e.g. golden Staph). Using honeys sourced from around Australia and screened against several reference microorganisms, the anti-microbial potency of one particular Australian honey (from Leptospermum polygalifolium) was shown to be comparable to NZ Manuka honey (from L.scoparium). The results of this screening of active honeys against pathogenic bacteria has supported the registration of honey by Capilano Honey Limited as a "Drug" with the Therapeutic Good Administration based on its antimicrobial activity.
This project was undertaken to add value to the existing honey resource by developing products with therapeutic benefit (i.e. for the treatment and management of moist wounds such as leg ulcers).
Specific geographic region(s) in Australia which produce "active" honey have been identified, the potency of the Leptospermum-derived honeys against a range of bacteria has been defined, the particular chemical characteristics of these honeys have been examined, and the honey has been registered as a "Drug" with the Therapeutic Good Administration. Work is continuing to better define the specific agents responsible for the antimicrobial activity (which have been elusive to date) and to evaluate the opportunity for therapeutic benefit from honey beyond its antimicrobial activity (i.e. its direct wound healing benefit).
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