Biofilms: The Hidden Culprit behind Chronic Wounds

Image obtained from https://advancedfunctionalmedicine.com.au/biofilms/ 

Why do some wounds heal quickly while others linger for months or even years? Why do they persist despite careful cleaning, changing of dressings and maybe even several courses of antibiotics? Slower healing wounds are linked to conditions like diabetes, poor circulation and ageing, where the body can’t repair itself as well. When these underlying problems persist, wounds can become stuck in a non-healing state, but growing evidence suggests that an additional factor may be at play. Research shows that special organised communities of bacteria called biofilms are commonly responsible for delayed healing.  

How do wounds normally heal? 

When the skin barrier is impaired, perhaps due to injury, a wound will form. The wound surface, lacking the protective barrier of the skin, is exposed to contamination with microbes. Bacteria from the skin around the wound and sometimes also from the environment, quickly settle on the wound surface in a process called colonisation (Mahoney, 2016). At this stage our immune system responds quickly as white blood cells arrive, control the bacteria and prevent them from causing an infection. As new tissue grows, the bacteria are maintained at low levels and gradually cleared as the wound closes and heals. Wounds are normally repaired within 3-14 days (Uberoi et al., 2024). 

If for some reason this process is disrupted, and the wound doesn’t heal and instead persists, a special colony of bacteria called a biofilm may start to develop inside the wound, preventing it from healing. Individuals with underlying conditions or weakened immune systems are particularly susceptible to chronic wounds. Pressure ulcers and diabetic foot are examples of wounds that commonly become chronic (Uberoi et al., 2024). 

What are biofilms? 

We can think of biofilms as communities of bacteria that have clumped together and produced a sticky shield around themselves for protection (Yin et al., 2019). A very common example of a biofilm is the plaque on your teeth, which builds up when bacteria attach to the tooth surface, protect themselves with a sticky coating and linger unless they are removed by brushing regularly (Rather et al., 2021). 

In the case of chronic wounds, this happens because the wound stays open and inflamed for a period of time that is sufficiently long enough to allow the bacteria to settle, attach firmly to the wound surface and build this protective coating around themselves, instead of being cleared by the immune system. When a wound is already slow to heal, the development of a biofilm makes it even harder for the body to repair itself, worsening the situation.  

How exactly do biofilms stop wounds from healing? 

In chronic wounds where bacterial biofilms are present, our white blood cells will sense bacteria and then gather at the wound site. This time however, they can’t effectively penetrate the sticky barrier of the biofilm and attack the bacteria inside. Ultimately, they struggle to clear the infection.  

The toxic substances our immune system releases in an attempt to kill the bacteria, damage the surrounding healthy tissue instead. This causes constant inflammation. As long as the bacteria persist, the immune system remains active and prevents the wound from progressing to the next stage of its healing. Research shows that instead of clearing the biofilm, the immune response in chronic wounds actually accelerates damage that supports growth of the biofilm. As a result, the wound stays stuck in a non-healing state (Hurlow et al., 2022). 

What about antibiotics? 

In many larger wounds, the standard care is to prescribe antibiotics to control infection. Unfortunately, biofilms are not only tolerant to our immune system, but also to antibiotics (Roy et al., 2018).  

How exactly do antibiotics work? Antibiotics are commonly used to treat infections. They target free-floating bacteria that are actively growing. It is in this replicating stage that bacteria are most vulnerable to the killing effects of antibiotics. On the other hand, biofilms are much harder to treat because their protective barrier stops antibiotics from reaching the bacteria, much like how it blocks the body’s immune cells. Bacteria in the biofilm are also in a sleep-like state where they are not actively growing, which means that they are not in the optimum state that antibiotics target (Roy et al., 2018).  

When antibiotics are used against biofilms, they will often kill only the most vulnerable bacteria that live in the outer layer of the biofilm community, leaving the stronger or more resilient ones alive. This contributes to a very prominent issue of antibiotic resistance, where the resulting bacteria can pass on their ability to resist antibiotics onto future populations of bacteria. Subsequent antibiotic courses are even less effective, making treatment options more limited. 

How do biofilm infected wounds differ from normal infections? 

It is important to highlight that a chronic biofilm-infected wound is not the same as an acute wound that has not yet healed. The bacteria in both are biologically different. In an acute wound, the bacteria are free-floating and therefore usually treatable with antibiotics, even when the infection has become more severe (Hurlow et al., 2022). A biofilm-infected wound on the other hand, contains bacteria that are stuck to the wound surface and surrounded by a sticky protective coating, and can’t be cleared by antibiotics alone. A common misconception is that biofilms are just infections that are in their later stage and are inevitably formed if a wound is neglected for long enough. However, specific conditions in the wound environment, usually created because of underlying conditions, are needed to create a biofilm. 

What are the best ways of dealing with biofilms? 

Importantly, the key to dealing with biofilms is to physically and mechanically remove them, much like how you would remove plaque on your teeth by brushing it off. The same is true of biofilms found in chronic wounds; application of antibacterial treatments alone are very often insufficient, and the biofilm needs to be physically taken away from the wound. This process is called debridement, where infected parts of the wound are removed (Hurlow et al., 2022).  

To prevent biofilm regrowth and to give the wound a healthy environment to foster healing, the wound bed must be kept fresh, moist and clean. This can be achieved through changing dressings regularly and keeping bacterial levels low. Dead or infected tissue can be removed surgically through debridement or using treatments like medicated dressings that gently and gradually break down the biofilm, helping reduce the bacterial load and encouraging the regrowth of healthy tissue (Wishnew, 2025).  

References 

Hurlow, J., & Bowler, P. G. (2022). Acute and chronic wound infections: microbiological, immunological, clinical and therapeutic distinctions. Journal of Wound Care, 30(5). 

Mahoney, K. (2016). Biofilms: the myths and realities. Wound Essentials, 10(2). Wounds UK. https://wounds-uk.com/wp-content/uploads/2023/02/content_11699.pdf 

Rather, M. A., Gupta, K., Mandal, M. (2021). Microbial biofilm: formation, architecture, antibiotic resistance, and control strategies. Braz J Microbiol, 52(4), 1701–1718. 

Razdan, K., Garcia-Lara, J., Sinha, V. R., & Singh, K. K. (2022). Pharmaceutical strategies for the treatment of bacterial biofilms in chronic wounds. Drug Discovery Today, 27(8), 2137–2150.  

Roy R, Tiwari M, Donelli G, Tiwari V.(2018) Strategies for combating bacterial biofilms: A focus on anti-biofilm agents and their mechanisms of action. Virulence, 9(1),522-554. 

Uberoi, A., McCready-Vangi, A., & Grice, E. A. (2024). The wound microbiota: microbial mechanisms of impaired wound healing and infection. Nat Rev Microbiol, 22, 507–521. https://doi.org/10.1038/s41579-024-01035-z 

Wishnew, J. (2025). Biofilms in chronic wounds: Why your wound isn’t healing. Dr  Wishnew. https://www.drwishnew.com/blog/biofilms-in-chronic-wounds-why-your-wound-isnt-healing 

Yin, W., Wang, Y., Liu, L., & He, J. (2019). Biofilms: The Microbial “Protective Clothing” in Extreme Environments. Int J Mol Sci, 20(14). 

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