Biofilms Directly Coat Collagen Fibers and Surfactants Can Remove Them

Introduction: Bacterial biofilms have been found in most chronic wounds. Physical removal and/or disruption are a common approach to treating wounds suspected of having bacterial biofilms.  

Purpose: We have sought to determine the underlying structure of biofilms and how a surfactant-based dressing affects it.

Materials and Methods: An ex vivo porcine skin explant model was used to establish a functional biofilm for 3 days.  The wounds were then treated with either a surfactants or with moistened gauze.  The wounds were wiped daily and had the surfactant re-applied.  Six explants per day from each group were harvested, bisected and analyzed by scanning electron microscopy (SEM) at ultra high magnification, and by immunofluorescent (IF) staining and confocal microscopy.

Results: Unlike some previous reports (1), we did not see any abscess-like structures in either the SEM or the confocal imaging.  Instead a common pattern of bacteria or antigen staining were found to coat the collagen fibers.  In the SEM, the gross outline of the fiber was visible, but not the individual fibrils.  After treatment with the surfactant, the individual fibrils were visible again.

Conclusions: Our findings challenge the existing ideas that biofilms are large, separate masses of bacteria found on the surface or imbedded in wounds.  Instead, they appear to limit their growth and attachment directly to the collagen matrix.  This also may explain the biofilm’s inhibition of healing, as the epidermis cannot “grab” the dermal matrix in the manner it needs to.  Finally, the surfactant was able to clearly remove and re-expose the dermal matrix collagen and thereby make it available to the healing cells.