In humans, biofilm is a well-known cause of delayed healing and low-grade inflammation of chronic wounds. In horses, biofilm formation in wounds has been studied to a very limited degree.

The objective of this study was thus to investigate the occurrence of biofilm in equine experimental wounds healing by secondary intention.

Tissue biopsies from non-contaminated, experimental excisional shoulder and limb wounds were obtained on day 1–2, day 7–10 and day 14–15 post-wounding. Limb wounds were either un-bandaged or bandaged to induce exuberant granulation tissue (EGT) formation and thereby impaired healing. Presence of biofilm in tissue biopsies was assessed by peptide nucleic acid fluorescence in situ hybridization (PNA FISH) and confocal laser scanning microscopy (CLSM).

Bandaged limb wounds developed EGT and displayed delayed healing, while shoulder and un-bandaged limb wounds healed normally. Biofilm was detected in limb wounds only. At day 14–15 biofilm was significantly more prevalent in bandaged limb wounds than in un-bandaged limb wounds (P = 0.003). Further, bandaged limb wounds had a statistically significant increase in biofilm burden from day 7–10 to day 14–15 (P = 0.009).

The finding that biofilm was most prevalent in bandaged limb wounds with EGT formation suggests that biofilm may be linked to delayed wound healing in horses, as has been observed in humans. The inability to clear bacteria could be related to hypoxia and low-grade inflammation in the EGT, but the interaction between biofilm forming bacteria and wound healing in horses needs further elucidation.