Biofilm is like a house that bacteria build that allows them to thrive and multiply on difference surfaces, e.g. teeth (termed plaque), orthopedic hardware, medical devices, and WOUNDS!  The community of microorganisms produce an extracellular polymeric substance composed of polysaccharides, extracellular DNA, and proteins that adheres to the surface of the wound and encases the microbes, thus preventing topical antimicrobial agents in wound dressings and systemic antibiotics from reaching them.[1]  Although the biofilm is polymicrobial, the first bacteria begin the following 5-step process of biofilm formation:

1. Reversible attachment of the microbe to the wound surface with pili, flagella, or other surface appendages or specific receptors
2. Irreversible attachment of the microbes mediated by the secretion of the exo-polysaccharide substance
3. Cell proliferation resulting in a microcolony that continues to proliferate
4. Growth and differentiation resulting in a mature biofilm community
5. Dispersion of biofilm cells by active or passive detachment.[2]

The biofilm can be invisible or it can appear as a yellow slimy film on the wound surface.  Even when invisible, the lack of healing response to standard care can be evidence of the biofilm presence.  Because of its adherent sticky composition, biofilm cannot be removed from the wound bed by mere mechanical cleansing.  Only bacteria on the surface are removed, but the “house” structure protects the bacteria; likewise, antimicrobial agents (e.g. silver, iodine) reach only the bacteria on the outer surface of the biofilm, not the ones protected inside.  Removal of the biofilm is a vital component of wound bed preparation and has been the focus of much research.  The strategies available to the practicing clinician are the following:

• Sharp and/or surgical debridement
• Hydrosurgical debridement using a high-powered parallel waterjet (Versajet, Smith & Nephew, Largo, Fl), an FDA approved medical device that focuses a high-powered stream of sterile saline into a high-energy cutting tip.  This waterjet can be used to remove superficial non-viable tissue, including biofilm, leaving a clean viable wound surface that is then treated with standard moist therapy.[3]
• Low-frequency contact ultrasound[4], ultrasound technology that produces highly focused ultrasonic energy that fragments or liquefies nonviable tissue (including biofilm) from the surface of the wound, also leaving a clean viable wound surface that is treated with standard moist therapy
• Hypochlorous acid (HOCl, Vashe Wound Solution, Urgo Medical, Fort Worth, TX), a wound cleanser that breaks down the polysaccharide portion of the protective biofilm matrix, thus allowing access to the bacteria inside for mechanical removal and thereby decreasing the bacterial burden on the wound¹
• Hydrofiber® dressing (Aquacel Ag Extra, ConvaTec, Bridgewater, NJ), a specialty dressing that disrupts the biofilm surface, absorbs the wound exudate, and thus allows the silver ions to attack the underlying microbes[5]

Swab cultures performed prior to removal of biofilm only capture the presence of microbes on the surface and are not sufficient to detect all of the bacteria that are interfering with wound healing.  It is imperative to first destroy the house that the bacteria build, then identify the offending pathogens living inside the house, and treat appropriately with topical antimicrobial strategies and/or systemic antibiotics based on deeper cultures.  This approach to wound bed preparation will help achieve the optimal outcome of complete wound healing.

[1] Robson MC. Disruption of biofilm with Vashe wound solution.  Wounds. 2019;10:S59-S60.

[2] Stoodley P, Sauer K, Davies DG, Costerton JW.  Biofilms as complex differentiated communities.  Annu Rev Microbiol.  2002;56:187-209.

[3] Weir D, Scarborough P. Wound debridement.  In In Hamm R (Ed), Text and Atlas of Wound Diagnosis and Treatment: 2^nd edition.  New York: McGraw Hill Education.  2019,349-371.  Available at https://accessphysiotherapy.mhmedical.com/book.aspx?bookid=1334. 

[4] Murphy CA, Houghton P, Brandys T, Rose G, Bryant D.  The effect of 22.5 kHz low-frequency contact ultrasound debridement (LFCUD) on lower extremity wound healing for a vascular surgery population: A randomized controlled trial.  Int Wound J. 2018;15(3):460-472.

[5] Bowler PG, Parsons D.  Combatting wound biofilm and recalcitrance with a novel anti-biofilm Hydrofiber® wound dressing.  Wound Medicine. 2016:14(9):6-11.