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Johns Hopkins University
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November 13, 2007
FOR IMMEDIATE RELEASE
MEDIA CONTACT: Mary Spiro
JH Institute for NanoBioTechnology
Survive Hostile Zones
Microfluidic Device May Reveal Ways to
Fight Antibiotic-Resistant Biofilms
Using an innovative device with microscopic chambers, researchers from four institutions, including Johns Hopkins, have gleaned important new information about how bacteria survive in hostile environments by forming antibiotic- resistant communities called biofilms. These biofilms play key roles in cystic fibrosis, urinary tract infections and other illnesses, and the researchers say their findings could help in the development of new treatments and preventive measures.
"There is a perception that single-celled organisms are asocial, but that is misguided," said Andre Levchenko, assistant professor of biomedical engineering in The Johns Hopkins University's Whiting School of Engineering and an affiliate of the university's Institute for NanoBioTechnology. "When bacteria are under stress which is the story of their lives they team up and form this collective called a biofilm. If you look at naturally occurring biofilms, they have very complicated architecture. They are like cities with channels for nutrients to go in and waste to go out."
Photo by Will Kirk
In the article, the researchers from Johns Hopkins; Virginia Tech; the University of California, San Diego; and Lund University in Sweden reported on the observation of the bacteria E. coli growing in the cramped conditions of a new microfluidic device. The device, which allows scientists to use nanoscale volumes of cells in solution, contains a series of tiny chambers of various shapes and sizes that keep the bacteria uniformly suspended in a culture medium.
Levchenko and his colleagues recorded the behavior of
single layers of cells using real-time microscopy.
Computational models validated their experimental results
and could predict the behavior of other bacterial species
under similar pressures. "We were surprised to find that
cells growing in chambers of all sorts of shapes gradually
organized themselves into highly regular structures,"
Levchenko said. "The computational model helped explain why
this was happening and how it might be used by the cells to
increase chances of survival."
Photo by Will Kirk
The microfluidic device, which was designed and fabricated in collaboration with Alex Groisman's laboratory at UCSD, allows the cells to flow freely into and out of the chambers. Test volumes in the chambers were in the nano- liter range, allowing visualization of single E. coli cells. Ann Stevens' laboratory at Virginia Tech helped to generate new strains of bacteria that permitted visualization of individual cells grown in a single layer.
Hojung Cho, a Johns Hopkins biomedical engineering doctoral student from Levchenko's lab and lead author of the journal article, captured on video the gradual self- organization and eventual construction of bacterial biofilms over a 24-hour period, using real-time microscopy techniques. The experiments were matched to modeling analysis developed in collaboration with Cho's colleagues at Lund. Images were analyzed using tools developed with the participation of Bruno Jedynak of the Johns Hopkins Center for Imaging Science.
Observation using microscopy revealed that the longer the packed cell population resided in the chambers, the more ordered the biofilm structure became, Levchenko said. Being highly packed in a tiny space can be very challenging for cells, so that any type of a strategy to help colony survival can be very important, he adds.
Levchenko also noted that rod-shaped E. coli that were too short or too long typically either did not organize well or did not avoid "stampede-like" blockages toward the exits. The shape of the confining space also strongly affected the cell organization in a colony, with highly disordered groups of cells found at sharp corners but not in the circular shaped microchambers.
Photo by Will Kirk
"You can put a patient on antibiotics, and it may seem that the infection has disappeared. But in a few months, it reappears, and it is usually in an antibiotic-resistant form," Levchenko says. To explore possible treatments, Levchenko said, the microfluidic device could be used as a tool to rapidly and simultaneously screen different types of drugs for their ability to prevent biofilms.
This research was supported by funding from the National Science Foundation, the National Institutes of Health and the Swedish Research Council.
Color images of Levchenko, Cho and the microfluidic device available; contact Mary Spiro.