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Background
Burn wounds
Burn wounds occur when the skin becomes too hot or too cold. This means that if you touch something in a freezer that is -80°C, you can burn your hand just as you would touching boiling water. Because low temperatures which can cause burns, are very rare in nature, those wounds were not recognized as burns until relatively recently, and we associate burns with high temperatures1.
As most people already know there are several degrees of burns. The most common one is a first degree burn wound. An example of a first degree burn wound is a sun burn. Tour skin barely gets damaged but may become red and soar (see figure 1). No treatment is needed for this type of burn, it will mostly heal by itself.
Figure 1:
A first degree burn wound 2
Secondly there are second degree burns. These burns can be divided in two categories namely superficial and deep second degree burns. Superficial second degree burns damage the top layer of the skin, the epidermis (See figure 2A). In this part of the skin, there are no blood vessels or nerves. Blood still flows through the skin, and you can still feel pain in the burnt skin. Superficial second-degree burns do not damage the basal lamina. The skin regenerates from the basal lamina upward.
Figure 2:
A superficial second degree burn wound. B. A deep second degree burn wound.2
Deep second degree burns go down to the middle layer of the skin, the dermis (See figure 2B). The dermis contains nerves and blood vessels. Deep second degree burns partially damage the basal lamina. Thus nerves, blood vessels and the regenerating part of the skin can be damaged. The sense of touch can be decreased in the burn, the skin loses fluid through blood loss and regeneration is slowed. These burns are more severe and cause open wounds, but no severe nerve damage has occurred yet. For this type of burn wounds, skin transplantation is a frequently used therapy. Of course it will take some time after skin transplantation for the wound to heal. Within this time, there is a high risk on getting infections. Mainly because your normal skin flora is burned, this decreases your natural protection and makes it easier for the pathogens to infect the wound.
Third degree burns go all the way to the subcutaneous tissue (See figure 3). The basal lamina is lost, and regeneration is not possible except for the edges of the wound where there still is some basal lamina.
Figure 3:
A third degree burn wound.2
The worst type of burn wound is the fourth degree burns because it goes further down into the muscles and organs and severe damage can occurs2.
The problem
Apart from skin transplantation there are almost no effective treatments available. Because deep second degree burn wounds have an increased risk on getting infected, caused by the depleted skin flora and the long healing periods, burn wounds are often preventative treated with antibiotics3. The reason for this is that the pathogens infecting the wound are hard to get rid of. Also the wounds are treated with bandages after skin transplantation but those need to be replaced several times a day. Which causes inconvenience for the patients and a lot of heavy work for the nurses.
Infections in burns are almost always caused by Pseudomonas aeruginosa and/or Staphylococcus aureus4. These pathogens can be antibiotic resistant, and if this is the case the patient can only undergo some ineffective treatments like bathing. Furthermore, if the pathogens enter the blood stream the patient becomes septic and will almost certainly die5.
Due to the increase in antibiotic resistance by pathogens, the antibiotic treatment for burn wounds is at risk of becoming more and more ineffective. Therefore a demand for new treatment methods arises.
References
1. Held M., Rothenberger J., Schiefer J., Rath R., Petersen W., Jaminet P., Schaller H.E., Rahmanian-Schwarz A., Alteration of biomechanical properties of skin in acute cold contact injury. Burns. 2014, volume 40, issue 7, p1384-1389.
2. Nederlandse Brandwonden Stichting, http://brandwondenstichting.nl/brandwonden-voorkomen/wat-zijn-brandwonden/ , Last visited: 17-10-2014.
3. Carrougher, G., Burn Wound Assessment and Topical Treatment, Carrougher, G. Burn Care and Therapy, Mosby, Missouri, 1998, p133-165.
4. Williams, W., Pathophysiology of the burn wound, in Herndon. Total Burn Care. 2nd edition Saunders, London, 2002, p514-521.
5. F.N. Williams, D.N. Herndon, H.K. Hawkins, J.O. Lee, R.A. Cox, G.A. Kulp, C.C. Finnerty, D.L. Chinkes and M.G. Jeschke. The leading causes of death after burn injury in a single pediatric burn center. Critical Care 2009, volume 13 p183.
Figure 4:
Lactococcus lactis
Lactococcus lactis
Lactococcus lactis is well-known in basic microbiology, genetics, molecular biology, as well as in food science and biotechnology. Lactococcus lactis, is currently very important for industrial fermentations, especially dairy products. In 1909 this bacterium became also known as Streptococcus lactis. And only until recently it was renamed and clearly separated from the genera of streptococci again1.
Food approved
L. lactis is generally known to be safe for human consumption2, and they have never been identified as a cause for infectious disease. Because of this fact, this bacterium is used in large quantities in the dairy industries in the production of many different products like cheese and buttermilk.
Characteristics
L. lactis is a gram-positive bacterium with non-motile, round-shaped cells which does not form spores. Depending on their growth conditions they typically appear to be 0.5-1.5µm in size. A characteristic of the L. lactis that makes them different then members of the Streptococcus genus, is that these species grow in pairs or in short chains, unlike the long chains that the Streptococcus species form.
Lactococci are found associated with plant material, mainly grasses, from which they are easily inoculated into milk. In order to be able to grown inside dairy products L. lactis relies on the degradation of dairy proteins into peptides. This bacterium uses enzymes to degrade the proteins to produce energy molecules (ATP) from lactose (or other dairy proteins). The byproduct of this process, lactic acid, is very important in fermentation and cheese productions. Also the lactic acid produced by the bacterium lowers the pH of the product and preserves it from the growth of unwanted bacteria and molds2.
Furthermore L. lactis is capable of producing nisin, an antibiotic-like substance, called a bacteriocin. It is a natural antimicrobial agent with activity against a wide variety of Gram-positive bacteria, including food-borne pathogens such as Listeria, Staphylococcus and Clostridium by targeting the cell membrane. Nisin is a natural preservative present in cheese and it is also used as a preservative in heat processes and low pH foods3.
Why L. lactis?
L. lactis was chosen for multiple reasons. To begin with we want to use the bacteria inside the active layer in the bandage, for this reason it is very important that the bacteria does not form spores since those can not be killed and escape our bandage. The second beneficial feature is that some strains in nature already produce nisin, a bacteriocin that can kill gram-positive bacteria. Thirdly it is considered a safe microorganism, and already widely used in food products. This increases the social acceptance of the use of a bacteria to fight other bacteria.
Also there is a group at molecular genetics within our university working with L. lactis, therefore it was possible to seek advice when needed.
At last we doubted about the use of L. lactis in our bandage because of the lactic acid production but after doing some research we even found some benefits in this. For example lactic acid is used to preserve food, which means it has an antimicrobial effect as mentioned before. This might help us fight the pathogens. To support this theory we found that wounds tolerate certain lactic acid concentrations without disturbing the wound healing4. Furthermore we found that lactic acid bacteria can even stimulate wound healing by up regulating certain neuropeptides5.
Shortly said it seemed like the perfect bacteria/chassis for our bandage.
References
1. Leonor Valdez-Sanchez, Lactococcus lactis, http://web.mst.edu/~microbio/bio221_2005/L_lactis.htm. Last visited: 17-10-2014.
2. European Food Safety Authority (EFSA), Parma, Italy. Scientific Opinion on the safety and efficacy of Lactococcus lactis (NCIMB 30160) as a silage additive for all species. EFSA Journal 2011volume 9 issue 9, p2366.
3. Kenneth Todar. Lactococcus lactis: nominated as the Wisconsin State Microbe. Online textbook of microbiology, UW Department of Bacteriology, www.textbookofbacteriology.net Last visited: 17-10-2014.
4. Britland S., Ross-Smith O., Jamil H., Smith A.G., Vowden K., Vowden P. The lactate conundrum in wound healing: clinical and experimental findings indicate the requirement for a rapid point-of-care diagnostic. Biotechnol Prog. 2012, volume 28, issue 4, p917-924.
5. Theofilos Poutahidis, Sean M. Kearney, Tatiana Levkovich, Peimin Qi, Bernard J. Varian, Jessica R. Lakritz, Yassin M. Ibrahim, Antonis Chatzigiagkos, Eric J. Alm, Susan E. Erdman. Microbial Symbionts Accelerate Wound Healing via the Neuropeptide Hormone Oxytocin. Plos one, Published: October 30, 2013.
