Bacteria like to clump together and cling to surfaces, where they secrete bits of molecular debris that grow into a slimy protective coating.

These gooey collections of bacteria are called biofilms, and they can be found everywhere — on moist rocks in streams, inside water treatment plants, and even on your teeth, if you forget to brush.

But biofilms can increase the threat from dangerous forms of bacteria, such as Staphylococcus aureus, which causes antibiotic-resistant staph infections. Ganging up in biofilms makes them even more resistant to antibiotics than bacteria on their own.

And in small tubes similar to medical devices like IV tubes and catheters, Staphylococcus aureus bacteria rapidly form biofilm filaments and streamers that can clog them up, according to Princeton University researchers who study how biofilms behave in flowing liquids.

Understanding how biofilms behave in these devices is important in preventing hospital-acquired infections, a large fraction of which are associated with urinary or intravenous catheters.

Biofilms normally grow in thick layers on surfaces, says Howard Stone, a professor of aerospace and mechanical engineering at Princeton University and co-author on the paper, which was published Friday in The New Journal of Physics. However, back in 2013, he and his group showed that in a flowing liquid, "biofilms rearrange and somehow form these string-like filaments that float up into the fluid."

They first observed these filaments when watching solutions of a different bacterium, Pseudomonas aeruginosa, flowing through winding microtubes. It took about 50 hours for the filaments to coalesce and clog the tubes.

But when they switched to Staphylococcus aureus bacteria, they were surprised at how quickly the filaments formed — in only a few hours.

They then tried coating the inside of the tubes with blood plasma, to better mimic the conditions inside medical devices, which are in contact with bodily fluids. The filaments clogged the tubes in a matter of minutes.

Biofilms of Staphylococcus aureus bacteria also clogged up materials of different shapes, such as branched networks of tubes.

Stone says he still isn't sure why the Staphylococcus aureus bacteria form these biofilm filaments so quickly, but the results may one day help engineers design medical devices that are more resistant to biofilms of infectious bacteria.

"If you recognize that the flow may be doing something to the biofilm," he told Shots, "you may think a lot more about both the types of devices that you make and the flow rates that you create inside."

But he cautions that a lot more work needs to be done first. The flow rates and bacterial concentrations they studied were higher than you would likely find in catheters and stents, and they only looked at systems in the lab — not in a medical setting.

Luanne Hall-Stoodley, a microbiologist at Ohio State University, says that studies like these begin to show us the true complexity of bacterial life forms — and how best to fight them.

"We thought we had figured out bacteria's Achilles' heel and we were going to beat them with antibiotics, but now antibiotic resistance is coming back to haunt us," she says.

"We have so underestimated the lowly bacterium."

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