Fundamentals, clinical relevance and wound cleansing in practice
Chronic, recurrent infections and stalled wound progression are part of everyday veterinary work. One possible factor is the organisation of the microorganisms involved into a biofilm. This article summarises the fundamentals and outlines the role wound cleansing can play in management.
What is a biofilm?
A biofilm is an organised community of microorganisms attached to a surface and embedded in a self-produced extracellular matrix (EPS). The matrix consists mainly of polysaccharides, proteins and extracellular DNA.
Development typically follows several stages:
- Attachment of individual microorganisms to tissue, foreign material or wound debris
- Formation of microcolonies and production of the EPS matrix
- Maturation into a three-dimensional structure
- Detachment of single cells, which can colonise new sites
Clinical relevance
Biofilms are associated with chronic and recurrent infections. In equine wounds, biofilms have been described microbiologically (Westgate et al. 2011).
Possible indications in daily practice include:
- a stalled wound despite appropriate management
- recurring coating or exudate
- relapse after systemic antibiotics are stopped
Reliable detection is difficult in practice. A standard culture reflects biofilm colonisation only to a limited extent.
How tolerance arises
Microorganisms in a mature biofilm are considerably more tolerant of antibiotics and many topically applied agents than free-living (planktonic) cells. This tolerance should be distinguished from genetically fixed resistance. Several mechanisms are discussed:
- Diffusion barrier: The EPS matrix can slow or limit the penetration of active substances.
- Reduced metabolic activity: Oxygen and nutrient gradients exist in the deeper layers, and cells there are less active. Many antibiotics target active cellular processes.
- Horizontal gene transfer: High cell density favours the exchange of resistance genes.
Management in veterinary practice
The foundation is veterinary assessment. This includes:
- clarifying the underlying condition and factors that impair healing (for example foreign bodies, implants, poor perfusion, endocrine disease)
- cytology, culture and, where appropriate, susceptibility testing
- mechanical or surgical debridement of devitalised tissue and coating
- regular wound irrigation and cleansing
- deciding on systemic antibiotics based on findings and indication
Debridement plays a central role in biofilm management. Irrigation and cleansing complement it. They remove loose coating, exudate and dirt, and make it easier to assess the wound bed.
Conclusion for practice
Biofilms are a relevant factor in stalled and recurrent wound and skin problems. Diagnostics, debridement and management of the underlying condition are decisive. Consistent wound cleansing is one part of an overall concept.
References
- Westgate SJ, Percival SL, Knottenbelt DC, Clegg PD, Cochrane CA. Microbiology of equine wounds and evidence of bacterial biofilms. Veterinary Microbiology. 2011;150(1-2):152-159. doi: 10.1016/j.vetmic.2011.01.003.