How Biofilm Affects Healing In Diabetic Foot Wounds
Chronic lower extremity wounds are a significant complication of diabetes. Approximately 15 to 20 percent of people with diabetes will develop a diabetic foot ulcer in their lifetime.1 As the number of people diagnosed with diabetes continues to rise, so will the number of diabetic foot ulcers. It is estimated that the number of people diagnosed with diabetes will double to an estimated 48 million people in the United States by the year 2050.1
Chronic diabetic foot ulcers that do not heal in a timely manner are more likely to be complicated by infection, hospitalization and amputation. Delayed wound healing is often complicated by the development of infection. Infection accounts for nearly 20 percent of all diabetes-related hospital admissions and also serves as a major risk factor for the development of non-traumatic amputation.1
It is vital that we attempt to develop treatment modalities and paradigms that promote effective wound healing, reduce the spread of infection and limit progression from wound development into lower extremity amputation.
Sheehan and colleagues studied the probability of complete wound closure in difficult to heal diabetic foot ulcerations.2 They found that monitoring the area of a wound over a four-week period is a strong predictor of healing rates at 12 weeks. The authors found this to be independent of the treatment modality utilized.
This landmark study helped set a standard to evaluate the rate of wound healing. The researchers concluded that ulcers that fail to decrease in size by approximately 50 percent over the first four weeks of treatment are unlikely to achieve wound healing in a reasonable amount of time.2
Panuncialman and Falanga have recently reviewed the science of wound bed preparation.3,4 They underscore the importance of debridement as a critical step in the transition of a chronic wound into an acute wound to expedite the healing process.
The role of bacteria in the healing or lack thereof in chronic wounds can be a controversial topic. Although one cannot achieve complete sterility of the chronic wound bed, control of bacterial burden, in terms of bacterial density and pathogenicity, is a goal in wound bed preparation along with the reduction of biofilm formation in these chronic wounds.
A Closer Look At The Science Of Biofilm
So what exactly is a biofilm and how does it have an impact on diabetic foot wounds? A biofilm is a polymicrobial sessile community of microorganisms that develop on the surface of chronic wounds. As the bacteria attach to each other and the wound surface, they produce an extra-polymeric substance that contributes to the structure of the biofilm. The depth of the biofilm can vary from a single cell layer to a thick community of cells surrounded by the extrapolymeric matrix. The biofilm forms a barrier around itself, making it very difficult for antimicrobial agents to penetrate it.
The science of biofilm and biofilm engineering have been active fields of study since the first description of sessile communities in 1978.5 Bacterial biofilms have gained increasing attention in recent years as their role in chronic wounds is becoming more apparent. Microbial biofilms have been implicated in up to 80 percent of human infections such as nephrolithiasis, endocarditis, cystic fibrosis, oral infections, chronic otitis media and infections associated with indwelling devices to name a few.6-8
Not everything is understood about the role of biofilms or the most effective way to get rid of them. What is understood is that biofilms play a significant role in chronic wounds.
In a study by James and co-workers, light microscopy and scanning electron microscopy revealed that 60 percent of chronic wounds contained a biofilm in comparison with only 6 percent of acute wounds.9 In acute wounds, bacteria is commonly in the planktonic form or free-floating, and does not have a complex structure as in a biofilm. These planktonic bacteria are often what a clinician obtains when performing a swab or culture of the wound.
However, the presence of biofilm may not be evident from simple wound cultures obtained and evaluated using traditional microbiological techniques. More sophisticated and expensive techniques such as light and scanning electron microscopy are required to evaluate for biofilm within a wound. Therefore, the presence of biofilms is difficult to identify and therefore often overlooked.6,10
In order to form a biofilm, the bacteria participate in a process called quorum sensing. In this process, the bacteria produce signaling molecules that diffuse across bacterial cell membranes and interact with receptors on the DNA, changing the phenotype of the bacteria.7
These complex communities of bacteria have evolved ways to communicate with each other through water channels. Through these channels, the bacterial colonies are able to up-regulate or down-regulate the transcription of genes and protein products that are beneficial to the biofilm and detrimental to the host by this phenomenon of quorum sensing. The water channels also carry bulk fluid into the community by convective flow and allow nutrients to enter and circulate. The channels are also a way for the buildup of wastes and toxins to exit.7,10
With the properties of the extracellular polymeric substance and the ability of quorum sensing, cells in the biofilm are able to change their proteome to exist in a sessile state with low metabolic levels and down-regulated cell activity.7,8 These factors contribute to the ineffectiveness of antimicrobial agents at penetrating the biofilm. Also bear in mind that since most antimicrobials work by altering processes in reproducing or metabolically active organisms, they are much less effective at eradicating biofilm due to their low metabolic activity.7,11
Studies have well documented the presence of biofilm as an important barrier to effective treatment. However, further studies are necessary to demonstrate what effectively eliminates biofilm formation in chronic wounds. It is essential to realize that biofilms are different from planktonic bacteria that are floating at or near the wound surfaces. Biofilms are embedded in a matrix material, have adopted a distinct biofilm phenotype and have formed interactive communities. Therefore, biofilms are extremely difficult to eradicate in comparison to the planktonic form.10
What You Should Know About Eliminating Biofilm
How can we clinically eliminate the presence of biofilm on a chronic wound? It is important to acknowledge that currently, no single strategy has proven to be consistently effective at suppressing the entire biofilm. Davis and colleagues state that there are four keys to prevent, reduce or treat biofilm formation.7 They include:
1) preventing the bacterial attachment;
2) disrupting the biofilm to allow penetration of topical antimicrobial agents;
3) interfering with quorum sensing; and
4) enhancing dispersion of bacteria from biofilms so the planktonic bacteria can be more easily destroyed.
What is on the horizon for effectively getting rid of the biofilm that inhabits chronic wounds? Several therapies are currently under investigation for their potential as antibiofilm agents. However, these are not yet available in clinical practice as the safety and efficacy of these therapies are still under examination. A few agents that are gaining momentum for their potential as antibiofilm agents include lactoferrin, xylitol, gallium and Dispersin B.6,7
Another viable treatment option may be the use of ultrasound debridement on the chronic wound. Researchers have suggested that ultrasound disrupts the quorum sensing that occurs within biofilms, thereby leading to decreased coordinated virulence.7 Although this treatment option has potential and would be a breakthrough for treating biofilm on chronic wounds, further studies are still needed to demonstrate the efficacy of ultrasonic debridement on the biofilm.
As the number of patients with diabetes continues to rise in the U.S., so too will the number of diabetic complications such as foot ulcers. It is becoming more apparent that the profession needs to pay greater attention to the role of biofilm in chronic wounds. Methods of biofilm eradication can encourage healing in a timely manner and avoid secondary complications, including infection, hospitalization and amputation in our high-risk diabetic population.
Dr. Cornell is currently doing a Fellowship in Diabetic Limb Salvage at Georgetown University Hospital in Washington, D.C.
Dr. Steinberg is an Assistant Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. Dr. Steinberg is a Fellow of the American College of Foot and Ankle Surgeons.
2. Sheehan P, Jones P, Giurini JM, Caselli A, Veves A. Percent change in wound area of diabetic foot ulcers over a 4-week period is a robust predictor of complete healing in a 12-week prospective trial. Plast Reconstr Surg 2006 Jun; 117(7Suppl):239S-244S.
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11. Martin JM, Zenilman JM, Lazarus GS. Molecular microbiology: new dimensions for cutaneous biology and wound healing. J Invest Dermatol 2010 Jan; 130(1):38-48.