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.
