Why Do Chronic Wounds Contain Biofilm?

The process of wound healing ideally progresses from inflammation to epithelialization and, finally, remodeling. If at any point bacterial (or fungal) colonization becomes prominent, the process of wound healing is disrupted. The creation of biofilm is a microbial defense mechanism that stalls the trajectory of healthy wound healing and can contribute to the development of a chronic wound. It is estimated that 90% of chronic wounds and 6% of acute wounds contain biofilms generated by microbes.^1,2 Epidemiologically, chronic wounds impact 2% of the entire US population.² Because of this large impact, knowledge of proper wound healing and use of clinical tools to assist the wound healing process are essential.

When Should I Assess for Biofilm?

Biofilm is not readily detected with the naked eye. However, the clinical index of suspicion should increase when any of the following are observed:³

1. Stalling of the normal healing process despite appropriate wound care and regular reassessment
2. The appearance of slough (and reappearance following debridement)
3. Secondary signs of infection (exudate, unpleasant odor, tenderness, reactive hyperemia around perimeter of wound, maceration)
4. Progressive necrosis around edge of wound bed (periwound)

How to Treat a Wound That Has Biofilm

When biofilm is thought to be present, medical intervention is indicated. This element of wound care generally involves debridement and wound cleansing, and finishes with the application of an appropriate dressing. The goal of this process is physical disruption of the biofilm layer in a way that minimizes mechanical trauma to healthy tissue. Bacteria, exudate, and cellular debris should be removed while limiting damage to healthy epithelialization of the wound bed. Once the biofilm is disrupted, cleansing solutions can penetrate the wound bed, thereby maximizing their potential efficacy. If signs of progressive infection are present, antiseptic cleansing solutions may be used as an adjunct to systemic antibiotics.³

What Are Some Antiseptic Cleansing Solutions Available?

After debridement of a chronic wound, there is a 24- to 72-hour window during which any lingering bacteria are sensitive to antimicrobial treatment.² During this period, application of an antiseptic cleansing solution is indicated. This will inhibit microbial cell-to-cell communication and prevent redevelopment of the biofilm.

The following types of antiseptic cleansing solutions are available:

• Povidone-iodine
• Chlorhexidine
• Sodium hypochlorite
• Octenidine dihydrochloride
• Polyhexamethylene biguanide (PHMB)

Povidone-iodine, chlorhexidine, and sodium hypochlorite are common types of antiseptic cleansing solutions. Other types of antiseptic solutions, such as octenidine dihydrochloride, are water based and are effective against methicillin-resistant Staphylococcus aureus (MRSA). Alternatively, there is PHMB, which is less cytotoxic than iodine and chlorhexidine. All antiseptic agents are known to cause irritation to healthy tissue. For this reason, following with a non-cytotoxic cleansing solution is recommended after each use of an antiseptic solution.³ Application of more than one antiseptic solution at a time is not appropriate. Antiseptic cleansing solutions should be used for up to 5 days but no longer than 14 days.³ After this time, reduced slough and/or odor should be observed, indicating a resolving infection.

When Should Non-Cytotoxic Cleansers Be Used? Saline and Surfactants

Once 5 to 14 days have passed, a “stepping down” of cleanser strength to a non-cytotoxic solution is appropriate.³ At this juncture, preservation of healthy viable cells and avoidance of damage to epithelializing tissue become the priorities. These goals are facilitated by gentle irrigation during dressing changes with non-cytotoxic cleansing solutions such as the following:

• 0.9% Normal saline (NS)

  This is the most commonly used non-cytotoxic cleansing solution in the health care setting. NS has the advantage of being isotonic, meaning it has the same physiologic osmotic pressure as blood. Additional features include availability in unit doses, half liters, liters, and even spray bottles. Regular opening of new, sterile containers reduces the likelihood of bacterial contamination, which can occur a container is if left open >24 hours.

• Lactated Ringer’s (LR)

  Like NS, LR is another commonly used isotonic solution. LR is similarly non-cytotoxic and features specific ions and salts, namely sodium (Na+), potassium (K+), and calcium chloride (CaCl2).

• Potable tap water

  This non-cytotoxic solution is the most easily accessible and cost-effective. Although tap water is not considered clinically sterile, a study comparing wounds cleansed with NS versus wounds cleansed with tap water found no significant difference in bacterial infections.³ Extra precaution is recommended, however, if bone or tendon is exposed: cleansing with potable water is not indicated under these circumstances. Finally, there is the potential for formation of wound edema resulting from the hypotonic nature of water. Prolonged exposure to the wound bed should be avoided.

• Dakin’s Solution

  This cleanser contains a dilution of the active ingredient hypochlorous acid(HOCL). Dakin’s Solution does not damage living cells in the wound bed and helps to separate dead tissue from healthy, viable tissue underneath. This non-cytotoxic cleanser has antiseptic properties and does not lose antimicrobial potency in the presence of blood serum or other bodily fluids.⁴

• Hypochlorous Acid (HOCL)

  This cleanser has been proven for years to promote the survival of fibroblasts and keratinocytes in the wound microenvironment. As a preservative in these solutions, HOCL has an effective and faster killing effect in vitro on a wide variety of microorganisms. These biochemical and biological factors indicate that a stabilized HOCL solution could be an effective wound care agent.

• Surfactants

  These cleansers are non-cytotoxic solutions with added utility for wounds that may contain contaminants. Each surfactant molecule has a hydrophilic head and a hydrophobic tail that simultaneously repel water and attach the molecule to debris, oils, and necrotic tissue. These opposing forces loosen particles within the wound and suspend the particles in water. A micelle is formed around such contaminants, thus allowing them to be removed with minimal force.⁵

All non-cytotoxic cleansing solutions listed here are recommended for use at physiologic body temperature (37° C). The reasoning for this is that cooling of the wound bed disrupts healing and epithelialization. Full leukocytic activity of white blood cells takes roughly 3 hours to return after cooling.³ If dressings and wound cleansing occur once every 24 hours, the cumulative delay to wound healing becomes significant, and the risk of infection increases. Regular reassessment of chronic wounds should occur at least once every 2 weeks for signs of improvement (or progression) of infection.

Conclusion

Biofilm is a major obstacle to healthy wound healing. If biofilm formation is suspected, debridement and mechanical disruption of the biofilm layer are indicated, followed by regular wound cleansing. Antiseptic solutions are useful at first, but cleanser potency should be "stepped down" after 5 to 14 days to a non-cytotoxic cleanser such as NS, LR, Dakin’s Solution, hypochlorous acid (HOCL), surfactants, or potable water. This process of biofilm treatment can help chronic wounds move further along the healing cascade.

References

1. Malone M, Bjarnsholt T, McBain AJ, et al. The prevalence of biofilms in chronic wounds: a systematic review and meta-analysis of published data. J Wound Care. 2017;26(1):20-25.
2. Dhar Y, Han Y. Current developments in biofilm treatments: wound and implant infections. Eng Regen. 2020;1:64-75.
3. Brown A. When is wound cleansing necessary and what solution should be used? Nurs Times. 2018;114(9):42-45.
4. Keyes M, Jamal Z, Thibodeau R. Dakin solution. In: StatPearls. StatPearls Publishing; 2022.
5. Percival SL, Mayer D, Malone M, Swanson T, Gibson D, Schultz G. Surfactants and their role in wound cleansing and biofilm management. J Wound Care. 2017;26(11):680-690.