How Biofilm Affects Healing In Diabetic Foot Wounds

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Rhonda Cornell, DPM

   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

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