Study Simulates How Medical Devices Are Rapidly Clogged by Bacteria
Princeton researchers used time-lapse imaging in a new study to examine how bacteria clog medical devices--which yielded a less pretty than usual time-lapse video. The microbes can be watched how they join to create slimy ribbons that tangle and trap other passing bacteria, creating a full blockage in a startlingly short period of time.
The researchers at Princeton University, who published their study in Proceedings of the National Academy of Sciences, monitored fluid flow in narrow tubes or pores similar to those used in water filters and medical devices. Unlike previous studies, the Princeton experiment more closely mimicked the natural features of the devices, using rough rather than smooth surfaces and pressure-driven fluid instead of non-moving fluid.
The team of biologists and engineers introduced a small number of bacteria that are known to be common contaminants of medical devices. Over a period of just 40 hours, the typical biofilm, a slimy coating, was formed on the walls by the microbes (colored green to identify them) as they multiplied. These films consist of thousands of individual cells held together by a sort of biological glue.
After this, the researchers sent additional microbes over the course of several hours, dyed red, into the tube. These red cells became stuck to the biofilm-coated walls, where the force of the flowing liquid shaped the trapped cells into streamers that rippled in the liquid like flags rippling in a breeze. During this time, the fluid flow slowed only slightly.
At about 55 hours into the experiment, the biofilm streamers tangled with each other, forming a net-like barrier that trapped additional bacterial cells, creating a larger barrier which in turn ensnared more cells. Within an hour, the entire tube became blocked and the fluid flow stopped.
The study was conducted by lead author Knut Drescher with assistance from technician Yi Shen. Drescher is a postdoctoral research associate working with Bonnie Bassler, Princeton’s Squibb Professor in Molecular Biology, and Prof. Howard Stone.
“For me the surprise was how quickly the biofilm streamers caused complete clogging,” said Stone. “There was no warning that something bad was about to happen.”
The researchers used stents, soil-based filters and water filters to prove that the biofilm streams indeed form in real scenarios and likely explain why devices fail.
The work allowed the researchers to explore which bacterial genes contribute to biofilm streamer formation. Previous studies, conducted under non-realistic conditions, identified several genes involved in formation of the biofilm streamers. The Princeton researchers found that some of those previously identified genes were not needed for biofilm streamer formation in the more realistic habitat.
Study:
Drescher, Knut, Yi Shen, Bonnie L. Bassler, and Howard A. Stone. 2013. Biofilm streamers cause catastrophic disruption of flow with consequences for environmental and medical systems. Proceedings of the National Academy of Sciences. Published online February 11.
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