New research by mechanical engineers at Purdue University, West Lafayette, IN, aims at fighting bacterial biofilms that can foul implantable medical devices. Bacteria secrete a slimy substance that forms biofilms, allowing bacterial colonies to thrive on surfaces, including catheters, prosthetic valves, and other devices. Combating biofilms using antibiotics and toxic chemicals can lead to the growth of antibiotic-resistant strains.

This graphic illustrates how swimming microorganisms cause the stretching of polymers in a mucus-like substance, attracting the motile cells to surfaces in biofilms. (Credit: Gaojin Li and Arezoo Ardekani)

The engineers’ findings reveal specifics about interactions that induce bacteria to swim close to surfaces, where they remain long enough to attach and form biofilms. They are learning how the swimming mechanics of microorganisms are affected by the exuded extracellular polymeric substance, which contains polysaccharides, proteins, and DNA polymers as they draw near surfaces.

The researchers studied the motion of motile organisms using a swimming model called a squirmer. The model allows them to use computers to simulate three modes of propulsion employed by the microorganisms: pulling or pushing themselves using flagella either in the front or back, respectively, and neutral, in which tiny cilia are located around a spherical organism.

They have discovered that most bacteria are “pushers”, and that pushers swim closer to surfaces in the presence of the extracellular polymeric substance. This knowledge could lead to methods that hinder the ability of bacteria to stick to surfaces.