The occurrence of biofilm in an equine experimental wound model of healing by secondary intention.

This research investigates the presence and impact of biofilm in equine (horse) wounds healing through secondary intention and observes a link between biofilm and delayed wound healing. The study further uncovers biofilm’s connection with exuberant granulation tissue (EGT) formation, which is associated with impeded wound healing.

Research Context and Objective

• While it is widely accepted in human medicine that biofilms – colonies of bacteria that adhere to living tissues – can delay healing and provoke low-grade inflammation in chronic wounds, such studies are limited in the case of equine wounds.
• The purpose of this study was to explore the occurrence of biofilm formation in equine wounds, observed in non-contaminated, experimental excisional shoulder and limb wounds, healing by secondary intention – a healing process where wound edges do not close, leading to a filling of the wound with granulation tissue.

Research Method

• Tissue biopsies were obtained from the wounds at three different stages of healing – day 1-2, day 7-10 and day 14-15 post-wounding.
• Some limb wounds were left un-bandaged, while others were bandaged to induce EGT – an overproduction of granulation tissue that impairs healing.
• The presence of biofilms in these biopsies was studied using peptide nucleic acid fluorescence in situ hybridization (PNA FISH) and confocal laser scanning microscopy (CLSM).

Results and Conclusions

• It was found that bandaged limb wounds that developed EGT showed delayed healing compared to un-bandaged limb wounds and shoulder wounds.
• Biofilm presence was noted only in limb wounds with significantly more biofilms in bandaged limb wounds than in un-bandaged ones (P=0.003).
• Furthermore, bandaged limb wounds displayed a statistically significant increase in biofilm load from day 7-10 to day 14-15 (P=0.009).
• The findings corroborated the human studies, showing that higher biofilm occurrence is associated with delayed wound healing in horses too, especially in wounds with EGT formation.
• The researchers suggest that the inability to clear bacteria from the wounds might be due to hypoxia and low-grade inflammation in the EGT, and further study is needed to understand the complex relationship between biofilm-forming bacteria and wound healing in horses.