Video: How do bacteria clog medical devices? Very quickly

Monday, March 4, 2013

A new study has exam?ined how bac?te?ria clog med?ical devices, and the result isn't pretty. The microbes join to cre?ate slimy rib?bons that tan?gle and trap other pass?ing bac?te?ria, cre?at?ing a full block?age in a star?tlingly short period of time.

The find?ing could help shape strate?gies for pre?vent?ing clog?ging of devices such as stents ? which are implanted in the body to keep open blood ves?sels and pas?sages ? as well as water fil?ters and other items that are sus?cep?ti?ble to con?t?a?m?i?na?tion. The research was pub?lished in Pro?ceed?ings of the National Acad?emy of Sciences.

Click on the image to view movie. Over a period of about 40 hours, bac?te?r?ial cells (green) flowed through a chan?nel, form?ing a green biofilm on the walls. Over the next ten hours, researchers sent red bac?te?r?ial cells through the chan?nel. The red cells became stuck in the sticky biofilm and began to form thin red stream?ers. Once stuck, these stream?ers in turn trapped addi?tional cells, lead?ing to rapid clog?ging. (Image source: Knut Drescher)

Using time-lapse imag?ing, researchers at Prince?ton Uni?ver?sity mon?i?tored fluid flow in nar?row tubes or pores sim?i?lar to those used in water fil?ters and med?ical devices. Unlike pre?vi?ous stud?ies, the Prince?ton exper?i?ment more closely mim?ic?ked the nat?ural fea?tures of the devices, using rough rather than smooth sur?faces and pressure-driven fluid instead of non-moving fluid.

The team of biol?o?gists and engi?neers intro?duced a small num?ber of bac?te?ria known to be com?mon con?t?a?m?i?nants of med?ical devices. Over a period of about 40 hours, the researchers observed that some of the microbes ? dyed green for vis?i?bil?ity ? attached to the inner wall of the tube and began to mul?ti?ply, even?tu?ally form?ing a slimy coat?ing called a biofilm. These films con?sist of thou?sands of indi?vid?ual cells held together by a sort of bio?log?i?cal glue.

Over the next sev?eral hours, the researchers sent addi?tional microbes, dyed red, into the tube. These red cells became stuck to the biofilm-coated walls, where the force of the flow?ing liq?uid shaped the trapped cells into stream?ers that rip?pled in the liq?uid like flags rip?pling in a breeze. Dur?ing this time, the fluid flow slowed only slightly.

At about 55 hours into the exper?i?ment, the biofilm stream?ers tan?gled with each other, form?ing a net-like bar?rier that trapped addi?tional bac?te?r?ial cells, cre?at?ing a larger bar?rier which in turn ensnared more cells. Within an hour, the entire tube became blocked and the fluid flow stopped.

The study was con?ducted by lead author Knut Drescher with assis?tance from tech?ni?cian Yi Shen. Drescher is a post?doc?toral research asso?ciate work?ing with Bon?nie Bassler, Princeton's Squibb Pro?fes?sor in Mol?e?c?u?lar Biol?ogy and a Howard Hughes Med?ical Insti?tute Inves?ti?ga?tor, and Howard Stone, Princeton's Don?ald R. Dixon '69 and Eliz?a?beth W. Dixon Pro?fes?sor of Mechan?i?cal and Aero?space Engineering.

"For me the sur?prise was how quickly the biofilm stream?ers caused com?plete clog?ging," said Stone. "There was no warn?ing that some?thing bad was about to happen."

By con?struct?ing their own con?trolled envi?ron?ment, the researchers demon?strated that rough sur?faces and pres?sure dri?ven flow are char?ac?ter?is?tics of nature and need to be taken into account exper?i?men?tally. The researchers used stents, soil-based fil?ters and water fil?ters to prove that the biofilm streams indeed form in real sce?nar?ios and likely explain why devices fail.

Biofilm streamers cause rapid and sudden clogging, as shown in this video of fluid flow through a microfluidic channel. Contrary to the current paradigm, the wall-attached biofilm that builds up over the first 55 hours only weakly affects the flow rate through the channel. Suddenly, biofilm streamers emerge, span the distance between corners in the channel, and rapidly expand to clog the channel. Credit: Knut Drescher, Princeton University

The work also allowed the researchers to explore which bac?te?r?ial genes con?tribute to biofilm streamer for?ma?tion. Pre?vi?ous stud?ies, con?ducted under non-realistic con?di?tions, iden?ti?fied sev?eral genes involved in for?ma?tion of the biofilm stream?ers. The Prince?ton researchers found that some of those pre?vi?ously iden?ti?fied genes were not needed for biofilm streamer for?ma?tion in the more real?is?tic habitat.

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Drescher, Knut, Yi Shen, Bon?nie L. Bassler, and Howard A. Stone. 2013. Biofilm stream?ers cause cat?a?strophic dis?rup?tion of flow with con?se?quences for envi?ron?men?tal and med?ical sys?tems. Pro?ceed?ings of the National Acad?emy of Sci?ences. Pub?lished online Feb?ru?ary 11.

Princeton University: http://www.princeton.edu

Thanks to Princeton University for this article.

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