PATHOGEN DETECTION/FOOD SAFETY: IR spectroscopy speeds E. coli detection

Infrared (IR) spectroscopy can detect E. coli faster than current testing methods and cut days off outbreak investigations, according to a study1 conducted at Purdue University.

Conventional techniques involving plating technology, which requires culturing cells in a laboratory, take 48 hours to produce results, but Lisa J. Mauer, an associate professor of food science, has demonstrated the ability to detect E. coli in ground beef in one hour. Mauer uses Fourier transform IR (FT-IR) spectroscopy, and explained to BioOptics World that she focuses in the mid-IR (4,000-650 cm-1), reading the spectrum created by the combination of energy that has been absorbed and energy that has been reflected back.

Purdue University researchers have demonstrated the ability to detect E. coli in one hour using infrared spectroscopy. This image of E. coli cells, captured by Colin Rickman of the Centre for Integrative Physiology at the University of Edinburgh (Scotland), was named an Image of Distinction in Nikon's Small World 2008 competition.

The technique not only identifies the bacteria, but also differentiates between strains of E. coli 0157:H7, allowing for outbreak tracking to be done more effectively and quickly. Current tests for differentiating strains involve multiple steps and can take almost one week to yield results. The methods also can differentiate between living and dead E. coli cells—something that current testing methods can't do. She notes that the presence of the dead population of E. coli cells could indicate the quality of the product.

Mauer has actually demonstrated two methods for separating bacteria from ground beef for testing: An antibody-capture method, which binds bacteria to antibodies attached to magnetic beads, gives results in four hours. A filtration method achieved results in about an hour. She claims that her FT-IR spectroscopy approach could be used in the same laboratories that now process cultures using the plating method.

Mauer believes the ground beef tests show promise for using the technology to find other pathogens in additional types of foods. She has already shown that spectroscopy can detect melamine (infamous for its inclusion in Chinese infant formula) down to one part per million in powdered baby formula. —Lee Mather

REFERENCE
1. L. Mauer et al., J. Food Sci. 75 (6): M340-46 (2010)

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