Rough Surfaces: Clinging to Crevices, E. coli Thrive


Photo: E. coli

Rather than being repelled by nanostructured surfaces, as materials scientists have hoped, bacteria with many flagella seem to love them;
© Harvard University

New research from Harvard University helps to explain how waterborne bacteria can colonize rough surfaces — even those that have been designed to resist water.

A team of materials scientists and microbiologists studied the gut bacterium Escherichia coli, which has many flagella that stick out in all directions. The researchers found that these tails can act as biological grappling hooks, reaching far into nanoscale crevices and latching the bacteria in place.

The scourge of the health care industry, bacteria like E. coli are adept at clinging to the materials used in medical implants like pacemakers, prosthetics, stents, and catheters, spreading slimy biofilm and causing dangerous infections. The findings suggest that antibacterial materials should incorporate both structural and chemical deterrents to bacterial attachment.

E. coli are equipped with two types of appendages: pili, which are short, sticky hairs, and the whip-like flagella, which are often twice as long as the bacterium itself. Pili had previously been recognized as playing a critical role in the formation of biofilms. These short hairs, up to only a micron in length in E. coli, can stick to surfaces temporarily, while the bacteria secrete a thick slime that holds them permanently in place.

Flagella, on the other hand, typically play a propulsive role, helping bacteria to swim and steer in liquid environments. As it turns out, though, when it is time to settle in one place, flagella also contribute to adhesion on rough surfaces, where the pili would have access to fewer attachment points.

Nanoscale crevices, such as those deliberately built into superhydrophobic materials, often trap air bubbles at the surface, which initially prevent E. coli from attaching at all. The new research shows that the bacteria can gradually force these bubbles to disperse by, essentially, flailing their arms. Once the cracks and crevices are wet, although the cell bodies cannot fit into the gaps, the flagella can reach deep into these areas and attach to a vast amount of new surface area.

"The diversity of strategies and methods by which bacteria can adhere reflects their need to survive in a huge variety of environments," says lead author Ronn S. Friedlander. "Of course, if we could prevent biofilms from forming where we didn't want them to, there would be immense benefits in medicine."; Source: Harvard University