Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - FIMBUG (Heterogeneity in fimbrial length and abundance as a generic regulator of E. coli surface colonization)

Teaser

Fimbriae are hair-like surface organelles found on many pathogenic bacteria. These structures are known to strongly promote formation of bacterial biofilms on tissue and biomaterials. This is an emerging problem in modern health care since biofilm implant-related infections...

Summary

Fimbriae are hair-like surface organelles found on many pathogenic bacteria. These structures are known to strongly promote formation of bacterial biofilms on tissue and biomaterials. This is an emerging problem in modern health care since biofilm implant-related infections are very difficult to eradicate and thus a main contributor to the development and spreading of antibiotic resistance.

The mechanisms by which fimbriae promote biofilm formation and spreading of antibiotic resistance genes are not well understood. A better understanding of these processes could aid development of new antibacterial and antibiofilm strategies, for example based on material design.

It is usually assumed that fimbriae provide bacteria with a way to form strong bonds to surfaces. However, several in vivo studies have shown that fimbriated bacteria that bind loosely to surfaces can form biofilms more efficiently. We hypothesized that this depends on the fact that a bacterium typically has many fimbriae (hundreds) and that it can bind with a variable number at a time. This way, bacteria may use fimbriae as a way to adjust their surface adhesion by shifting between monovalent, loose and mobile binding, to firm multivalent, immobile binding. We wanted to find out how this help E. coli bacteria to colonise surfaces and if it matters how many fimbriae the bacteria have.

We found that fimbriae provide bacteria with a generic way to sense and change binding behavior in response to environmental conditions like surface composition and liquid flow environment. Importantly, we found that this helped bacteria to find positions on a surface where nutrients were abundant, thus enhancing cell growth. It also governed the organization of the early biofilm so that bacteria can interact with each other. The latter was found to have a strong effect on the spreading of antibiotic resistance genes.

Work performed

In this project we have:

Developed a new approach combining nanopatterned surfaces with 3D holographic microscopy to enable the simultaneous measurements of the hydrodynamic forces acting on a bacterium and the resulting bacterial movements.

Detailed the mechanism of how fimbriated bacteria can undergo flow-modulated surface movements and force-enhanced binding on any surface.

Shown that multivalent binding provides bacteria with a mean to sense and respond in their binding strength, both to surface concentration of ligand and to variation in fluid forces.

Shown that fimbriae allow bacteria to adjust their position relative each other during cell growth, tuned by surface adhesiveness and flow forces.

Established that spread of antibiotic resistance via horizontal gene transfer of an IncP1 plasmid in a growing E. coli biofilm depend strongly on fluid forces. This could be directly related to the relative positioning of adjacent bacteria.

Evaluated different methods to genetically control the level of fimbriation in different E. coli strains and the mechanical properties of fimbriae.

Developed new label-free and non-destructive methods to characterize how many fimbriae bacteria have and how long they are.

Set-up and evaluated experiments that test the colonization fitness of bacteria in relation to level of fimbriation and underlying ecological processes that may have driven the evolution of these structure.

Results from this project has been presented at 6 international conferences and meetings. The project has also been presented several times in smaller settings at invited presentations locally and at different universities. Four popular science presentations have been performed mainly addressing last-year high school students. Manuscripts have been written that will be submitted for Open Access publications in peer-reviewed scientific journals.

Final results

The identified physiochemical mechanism by which bacteria use fimbriae to sense different surface conditions and respond to fluid forces is a breakthrough which may change the current view on why bacteria have fimbriae/pili and their involvement in bacterial biofilm formation.

In particular, we could identify a “missing link” in contemporary biofilm models by clearly showing that modulation of surface interaction, via fimbriae, may trigger adsorbed bacteria to express biofilm-specific phenotypes like EPS production and elevated transfer of antibiotic resistance genes. We expect these findings to impact future development of biomaterials and other smart materials.

Within FIMBUG several novel analytical methods and approaches have been developed. The ability to image the movements/deformation of a cell and the forces acting on it using holographic microscopy opens up for measurements under more realistic settings compared with atomic force microscopy or optical tweezers. We expect this to contribute broadly to an enhanced understanding of cellular binding, or other cellular processes. We also invented a new method to determine the number of fimbriae on bacteria. This method may be used in future diagnostic applications.

Website & more info

More info: https://cmb.gu.se/english/about_us/staff/.