Microrheology of Pseudomonas aeruginosa Biofilms Grown in Wound Beds*

Pseudomonas aeruginosa biofilms cause persistent, deadly infections in wounds due to their resistance to antibiotic treatments and physical removal. The biofilm’s viscoelasticity plays an important role in enabling it to thrive. Understanding the mechanisms causing biofilm viscoelasticity can aid in designing novel treatments.  Furthermore, it is necessary to establish how host proteins, such as collagen, in the wound bed affect viscoelasticity.

We explore how collagen affects biofilm viscoelasticity using particle tracking passive microrheology in both in vitro wound like models as well as through a novel ex vivo technique using unmanipulated biofilms grown in vivo in mouse wound beds.  To understand collagen interactions with biofilms, we study biofilms grown from a range of mutant strains of PAO1 P. aeruginosa that lack polysaccharide components of extra polymeric substance.  In vitro, collagen is seen to universally create more elastic and stiffer biofilms that exhibit less heterogeneity.  Data indicates that the free collagen incorporates into the biofilm through non-specific physical entanglement, which results in the changes to the biofilm viscoelasticity. Ex-vivo biofilms exhibit viscoelastic behavior similar to the in-vitro films grown in the presence of collagen, confirming our hypothesis regarding the importance of collagen to biofilm growth.  However, we note some differences with in vitro experiments with collagen, indicating additional interactions between host proteins and the biofilm.  Overall, these results indicate the importance of collagen on P. aeruginosa biofilms and that in-vitro viscoelasticity is not an ideal representation of in-vivo conditions.