Low-cost system for detection of bacteria.

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Researchers at Purdue University have developed a new low-cost system that analyzes scattered laser light to rapidly identify bacteria for applications in medicine, food processing, and homeland security--at one-tenth the cost of doing so with conventional technologies.

The optical-scattering that the researchers are using works by shining a laser through a petri dish containing bacterial colonies growing in a nutrient medium.

"Unlike with conventional methods, we don't have to do any biochemical staining, DNA analysis, or other types of manipulation," said Bartek Rajwa, a staff scientist at Purdue's Bindley Bioscience Center.

Particles of light, called photons, bounce off of the colony, and the pattern of scattered light is projected onto a screen behind the petri dish. This "light-scatter pattern" is recorded with a digital camera and analyzed with sophisticated software.

The work was initiated by Arun Bhunia, a professor of food microbiology in the Department of Food Science, and E. Daniel Hirleman, a professor and head of Purdue's School of Mechanical Engineering. Findings are detailed in a research paper that appeared in the May/June 2006 issue of the Journal of Biomedical Optics under the title "Feature Extraction from Light-Scatter Patterns of Listeria Colonies for Identification and Classification."

A major motivation for the research was to reduce the time it takes for industry to identify harmful organisms in food processing.

"The dairy industry, for example, grows bacteria on petri dishes to make sure products are safe, but industry is trying to develop technologies that will very quickly identify organisms," said J. Paul Robinson, a researcher at the Bindley Center and a professor at the Weldon School of Biomedical Engineering and the School of Veterinary Medicine. "The same sort of thing holds true for clinical microbiology and other laboratories. With our light-scattering method, it takes less than five minutes to identify harmful organisms after they have grown in a petri dish. The analysis is faster than any other methods in existence, and it's simple."

A mass-produced system based on the technology...

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