“Our findings strongly support the idea that biofilms are active biomaterials, that they have the ability to mechanically interact with their environments”Alice Cont

A team of researchers from Ecole Polytechnique Fédérale de Lausanne in Switzerland have shown how the mechanical forces of biofilms could work to spread infections. The study, which demonstrated how the biofilms of two major pathogenic bacteria can mechanically disrupt tissue, suggests they can damage their host without using toxins, and that any bacterial species that forms biofilms has the potential to damage host epithelia. Mechanical interactions between bacteria and their host may therefore be a contributor to infections and colonization.

In forming huge complex communities on surfaces, bacteria can result in chronic infections to humans. Although such interaction between these biofilms and the host is commonly thought to be biochemical, mechanical interplay between them could be a significant factor for the host’s physiology. In exploring the role of mechanics during bacterial infections, such as the stiffness of the infected tissue, synthetic hydrogels were here used to “mimic” this condition.

As reported in eLife [Cont et al. Elife (2020) DOI: 7554/eLife.56533], the team grew biofilms on soft hydrogel surfaces using the bacteria Vibrio cholerae and Pseudomonas aeruginosa. They then measured the forces they exerted on variations of extracellular polymeric substances (EPS), a matrix that relies on the bacteria attaching themselves to a surface and then dividing, while also burying inside a mix of polysaccharides, proteins and nucleic acids, as well as debris from dead cells.

Through combining mechanical measurements and mutations in matrix components, the biofilms were shown to deform by buckling, and that adhesion transmitted these forces to their substrates. On growing inside the EPS, single bacteria stretch or compress it, exerting mechanical stress. The development of growth on the biofilm, and also the elastic properties of the EPS matrix, produces internal mechanical stress.

V. cholerae biofilms were found to produce sufficient mechanical stress to deform and damage soft epithelial cell monolayers, indicating the forces from the growing biofilms could mechanically compromise the physiology of their host – ie, biofilms could promote a "mechanical" mode of infection, a breakthrough that could lead to innovative treatment of certain infections and metabolic diseases. As researcher Alice Cont told Materials Today,  “Our findings strongly support the idea that biofilms are active biomaterials, that they have the ability to mechanically interact with their environments”.

Further work could involve investigating the phenomenon in vivo, and the mechanism could be assessed through developing a more detailed physical model. Another avenue of investigation lies in analyzing whether the mechanical properties of the surface could impact bacterial behavior, not only from physical interaction but also “sensing” and patterns of gene expressions.

Biofilms growing on hydrogel surfaces. Credit: eLife
Biofilms growing on hydrogel surfaces. Credit: eLife