Alternate forms of antibacterial agents

The wound infection consensus document launched in Toronto by the World Union of Wound Healing Societies (2008) refers to honey, tea tree oil, and maggots as an alternative compared to the more traditionally recognized antimicrobials.

Honey

The earliest record of the use of honey in wound treatment is noted on a fragment of a clay tablet dated to approximately 4500 years ago. Honey stopped being used in modern medicine in the 1970s and was re-introduced in the 1990s when a new generation of wound care products was developed. Molan et al. (1999) highlight a number of components of medical-grade honey that make it effective as an antimicrobial which include (1) its hygroscopic effect (meaning it draws moisture out of the environment) due to its high sugar content, (2) the presence of hydrogen peroxide, (3) the low pH (acidic— mean 4.4), and (4) the Unique Manuka Factor (UMF®) with its associated antibacterial peptides in some honeys. Most unprocessed honeys produce antimicrobial hydrogen peroxide by the activation of the enzyme glucose oxidase, which oxidizes glucose to gluconic acid and hydrogen peroxide. However, hydrogen peroxide can be degraded by an enzyme catalase, which can be found in wound fluid.

Manuka (Leptospermum) honey is made from nectar derived from a standard mixture of different Leptospermum spp. The Leptosperum spp. of plants are known by a number common names in Australia and New Zealand including Tea Tree, Manuka, Goo bush, and Jelly bush and at least 79 species have been described (Molan 2001). Unlike many common honeys, peroxide activity is not lost in the presence of catalase and it retains activity. They are also known as non-peroxide honeys because there are other unidentified components that contribute to the antimicrobial activity. A descriptor of UMF® has been given to these components. The number that follows the UMF®, for example, 10, means that the honey is 10 times more active than the standard antiseptic. The highest recorded level is around 20.

> DEFINITION

Catalase is an enzyme that degrades hydrogen peroxide and is found in wound fluid.

) KEY POINT

Honeys used for wound care should be medically certified honeys licensed as a medical product for professional wound care and not ‘table honeys’ that can be purchased over the counter as these may contain bacteria

The physical properties of honey play a part in its effectiveness as a wound dressing. Because of its viscosity, honey is claimed to provide a protective barrier which prevents cross infection. Also, because of its osmolarity drawing fluid out of the tissues it helps cleanse wounds providing a moist healing environment. This also means that dressings may not stick to the surface of wounds as they sit on a layer of diluted honey. There appears to be no growth of new tissue into the dressing so minimal pain on removal is claimed to be achieved.

As with many wound healing agents few randomized trials exist on the clinical efficacy of honey to complement the plethora of publications that demonstrate laboratory efficacy and successful case outcomes following its use and some randomized controlled trials found in the literature do not show significant benefits (Jull et al. 2008).

Larval therapy

There has been renewed interest in the use of maggots in wound healing. Larvae of the medicinal blow fly species (Lucilia sericata) have created a niche in therapeutic options called biosurgery. They are easy to culture in sterile conditions, have convenient life cycles, and are relatively hardy, withstanding the harsh environment of wounds that may also contain drugs. In particular, they avoid feeding on live tissue and can also be cooled for transport in sterilized containers and stored at 5°C (Wounds UK 2013). They are provided in special gauze bags that allow them to reach the tissue being treated. Antimicrobial enzymes are secreted which digest necrotic tissue and this is absorbed by the maggot, leaving the wound bed clean. More recently, a peptide known as lucifesin has been purified from larval secretions and exhibits a high degree of potency against wound pathogens (Jaklic et al. 2008).

 
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