Rethinking Biofilms in Chronic Wound Care: Complexity, Misconceptions, and Clinical Pearls from SAWC Spring 2025
In a thought-provoking and myth-busting session at the Symposium on Advanced Wound Care (SAWC) Spring | Wound Healing Society (WHS) meeting, Lindsay Kalan, PhD, Associate Professor at the Infectious Disease Institute, McMaster University, challenged longstanding assumptions about biofilms in chronic wounds. Titled “Biofilms: What's True, What's Not”, the presentation provided an evidence-based reexamination of how clinicians should view, detect, and manage biofilms in clinical practice.
Biofilms: Not What We Think
Dr Kalan opened by urging clinicians to rethink their mental image of biofilms, which are often depicted as structured, mushroom-like colonies based on lab-grown Pseudomonas aeruginosa in petri dishes. “A petri dish is not human skin, it is not tissue, it is not in the environment,” she emphasized. In the real-world wound environment, biofilms are far less defined, highly heterogeneous, and frequently polymicrobial.
Are All Chronic Wounds Biofilm-Rich?
One of the most consequential takeaways from Dr Kalan’s research is that while nearly all chronic wounds are colonized by microbes, not all contain visible or structurally consistent biofilms. “Only 30% of the samples we analyzed actually had visible microbial aggregates,” she said, referring to detailed microscopy and molecular analyses of slough and wound tissue. Yet, bioburden remained universally high across samples, highlighting the inadequacy of current detection methods.
Debunking the Slough Myth
Clinicians often associate slough with biofilms, but Dr Kalan decisively debunked the notion that slough is predominantly composed of biofilm. “It’s a myth based on the evidence we currently have,” she stated. Her lab’s findings demonstrated that slough is highly variable and often contains complex material beyond microbial content, making visual assessment unreliable for diagnosing biofilm presence or predicting wound healing outcomes.
Mixed-Species Infections: A Complicating Factor
Kalan emphasized that microbial diversity in wounds adds further complexity. Mixed-species infections elicit different immune responses compared to single-species infections. In a striking example, human neutrophils exhibited increased cell death when exposed to co-cultures of Candida albicans and Citrobacter freundii versus either organism alone. “Their immune cells are reacting differently to the mixed species,” she explained, implying that this could contribute to the chronic inflammation often observed in nonhealing wounds.
Hidden Reservoirs and Recolonization
In ex vivo human skin models, Kalan’s team discovered that Pseudomonas bacteria could burrow deep into wound tissue, effectively evading topical antiseptics and recolonizing the wound surface after cleaning. “This is now a reservoir for them to reseed the wound bed once it's cleaned,” she warned, underscoring the limitations of conventional cleansing and debridement strategies.
Clinical Pearls for Practice
In closing, Dr Kalan offered 3 pivotal insights for wound care clinicians:
- Wounds are highly polymicrobial, regardless of healing status.
- Bioburden alone is not predictive of healing; microbial interactions and microenvironmental conditions must be considered.
- Biofilms are difficult to detect, and their absence by microscopy does not imply clinical irrelevance.
“This doesn’t mean we abandon good wound bed preparation,” she concluded. “But we must acknowledge that not everything is as we think. There’s still a lot we need to learn.”
Dr Kalan’s session called for a paradigm shift in biofilm research and clinical management, urging a more nuanced and evidence-based approach to wound microbiology.
