Elsevier

Burns

Volume 39, Issue 4, June 2013, Pages 754-759
Burns

The effect of a honey based gel and silver sulphadiazine on bacterial infections of in vitro burn wounds

https://doi.org/10.1016/j.burns.2012.09.008Get rights and content

Abstract

Bacterial contamination remains a constant threat in burn wound care. Topical treatments to combat contaminations have good bactericidal effects but can have detrimental effects for the healing process. Treatments with for example silver can increase healing times. Honey based products can be a good alternative as it is antibacterial and patient-friendly.

We evaluated the bactericidal and cytotoxic effects of a honey based gel and silver sulphadiazine in a human burn wound model with Pseudomonas aeruginosa. After adding 105 colony forming units of P. aeruginosa, topical treatments were applied on the burn wound models. After 2, 12, 24, 28 and 70 h, bacteria were dislodged and counted by plating dilutions. Cytotoxic effects were evaluated histologically in samples of burn wound models treated topically for 3 weeks, without bacteria.

l-Mesitran Soft significantly reduced the bacterial load (5-log reduction) up to 24 h but did not completely eliminate bacteria from the burn wounds. After Flammazine® treatment, only a few colony forming units were observed at all time points. In contrast, re-epithelialization was significantly reduced after application of Flammazine® compared to l-Mesitran Soft or control.

This in vitro model of burn wound infection can be used to evaluate topical treatments. l-Mesitran Soft is a good alternative for treating burn wounds but the slightly lower bactericidal activity in the burn wound model warrants a higher frequency of application.

Introduction

Despite significant improvement in the survival of burn patients, infectious complications continue to be a major cause of morbidity and mortality. Burn patients are at high risk of wound infection, sepsis, and ventilator-associated pneumonia because of reduced immune responses. A predominant pathogen cultured from burn wounds in most centres is Pseudomonas aeruginosa [1], [2], [3], [4], [5], [6]. P. aeruginosa is an opportunistic pathogen, which takes advantage of the compromised defence mechanisms in burn patients, namely due to the loss of skin barrier and the suppression of the innate and adaptive immune system [7], [8], [9], [10], [11], [12]. P. aeruginosa infections in burn patients have been associated with mortality rates of up to 80% [13]. The morbidity associated with P. aeruginosa infections is mediated by a combination of several virulence factors such as lipopolysaccharide and haemolysin [14]. Due to its (multi)drug resistance, its abilities to form biofilms and to survive in many hostile environments, P. aeruginosa is difficult to eradicate from burn wounds [7], [15], [16], [17].

Systemic antibiotics can be used but are less favourable because of the low penetration rate into dead tissue and the risk of resistance development. To combat burn wound infections, many different antiseptics are available. Topical treatments have good bactericidal effects but can have detrimental effects on the healing process [18].

With any wound dressing a balance must be obtained between antimicrobial efficacy and cytotoxicity. The antimicrobial effect of antiseptics is accompanied by cytotoxic side effects [19]. Medical specialists are still challenged in finding the optimal treatment for difficult-to-heal wounds, e.g. ulcers, trauma induced wounds and deep burns. Open wounds are susceptible to invading pathogens such as bacteria and fungi. Therefore, optimal wound healing is dependent on the type of antiseptic medication used in combination with the method of wound closure.

Silver-containg dressings and topical silver agents represent one of the current standards for the treatment of superficial and deep dermal burns, because silver is an effective, broad-spectrum antimicrobial agent [20], [21], [22], [23]. Resistance to silver can occur in some bacterial species albeit only to a low level [22], [24]. Various reports however suggest that silver-sulphadiazine delays wound healing by enhancing the proinflammatory cytokines and that its use may lead to poor scarring [25], [26], [27]. Despite advantages as reduced use of systemic antibiotics and slow release of silver ions in order to promote healing, cellular toxicity remains a problem. Silver sulphadiazine is only to be used for a limited period in the treatment of burns rather than for the entire treatment period. Silver sulphadiazine was found to be cytotoxic for human skin and skin subsitutes [18], [28]. Topical silver might delay wound healing, because of its toxicity to keratinocytes [29]. However, whether silver is detrimental for keratinocytes is still under debate [30]. Based on the recent and thorough systematic review and meta-analysis of 14 RCT's by Aziz et al. it can be concluded that the evidence for infection prevention as well as inducing of healing is contradictory and limited due to the small number of well-designed and well conducted comparative studies [31]. Although in general the antimicrobial effect of silver is not under debate, no conclusion can be reached based on current literature as to the right dosage of silver in vivo in wound management [32].

Another approach in this area is the development of dressings with a controlled release of antibiotics or biocides. This strategy allows high levels of antibiotic drugs to specifically reach the wound area and avoids the disadvantage of current antimicrobial creams and ointments that need frequent dressing changes. Although promising results have appeared recently in the literature [33], these data are still from an experimental setup and no clinical data have been presented so far. Clinical results with biocide impregnated dressings indicate a need for improvement on infection prevention and clinical outcome (healing time) [34], [35].

A good alternative to silver based dressings might be honey, which has no adverse effects on wound healing. Honey has been used as a topical treatment for infection throughout history [36]. Honey may improve healing times in mild to moderate superficial and partial thickness burns compared to some conventional dressings [29], [37]. Honey also appears to be effective in wound deodorizing and debridement; it has an anti-inflammatory effect and can stimulate tissue growth [38]. The antimicrobial properties of honey are mediated by hydrogen peroxide, high sugar content, low pH, methylglyoxal and bee defensin-1 [39]. Activation of enzymes in the host and the osmotic ability of honey both stimulate autolysis of necrotic tissue [38]. Honey promotes the formation of healthy granulation tissue [38], optimizes epithelialization [38] and angiogenesis [40], and oxygen uptake is induced. Hydrogen peroxide is produced by glucose oxidase in honey and stimulates the growth of fibroblasts and epithelial cells [41]. This all contributes to the promotion of tissue regeneration.

Because honey in its pure form is not patient-friendly (e.g. it runs off the body when warm), l-Mesitran Soft was developed. This anti-bacterial gel can be used to manage a variety of (chronic) wounds in a wide range of stages of the healing process. The antibacterial effect of honey and l-Mesitran Soft has been shown in vitro [27], [29], [39], [42] but not yet in a burn wound model based on human skin. Also, the effects of l-Mesitran Soft on burn wound healing have not been shown in vitro.

In this study we investigated the bactericidal effect of l-Mesitran Soft on P. aeruginosa in a human burn wound model. For comparison, we used a silver sulphadiazine cream (Flammazine®), which is being used in Dutch burn centres. In addition, we tested the effect of these topical treatments on re-epithelialization.

Section snippets

Materials

l-Mesitran Soft (Triticum Group, Maastricht, The Netherlands) is a gel that contains 40% honey, hypoallergenic lanolin, vitamin C, vitamin E and polyethylene glycol 4000.

Burn wound model

Human skin was obtained from 13 healthy donors undergoing dermolipectomy, or from 11 deceased donors via the Euro Tissue Bank (Beverwijk, The Netherlands), after obtaining consent according to institutional guidelines. The burn wound model was performed as described by Coolen et al. [43]. A split-thickness skin graft (0.5 mm

In vitro model of burn wound infection

Infection of the burn wound model with 105 CFU of PAO1 resulted in biofilm-like growth on the epidermis, which expanded to the edges of the epidermis. At that location, bacteria translocated into the dermis and proliferated in between the dermis and the epidermis (Fig. 1). The epidermis was clearly affected by PAO1, leading to detachment and destruction of the epidermis. After 3 days of culture, the skin sample was completely colonized. Longer incubation times were not possible because of growth

Discussion

We investigated bactericidal activity and effect on re-epithelialization of both l-Mesitran Soft and Flammazine® in our burn wound model. Bactericidal activity of l-Mesitran Soft in the burn wound model seems to be less effective in comparison with Flammazine®. However, the viscosity of l-Mesitran Soft is lower than that of Flammazine®, it spreads more easily on skin and is therefore easier diluted. This might have resulted in a lower concentration and activity. Application of l-Mesitran Soft

Conclusion

We have shown that this in vitro model of burn wound infection can be used to study the effects of topical treatments. Application of l-Mesitran Soft resulted in significantly more re-epithelialization compared to Flammazine®. The slightly lower bactericidal activity in the burn wound model warrants a higher frequency of application of l-Mesitran Soft.

Disclosure

This work was financially supported by the Triticum Group, Maastricht, The Netherlands.

Conflict of interest

None of the authors have any financial and personal relationships with other people or organizations that could inappropriately influence (bias) this work.

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