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New technique promises faster detection of food poisoning bacteria


A new method that establishes genetic markers for bacteria in water, food, and biological and medical samples could be used to detect terrorist contamination, or simply the bacterial contamination that causes food poisoning.

The patented system, developed by researchers in Israel, uses the genetic material in bacteria such as E. coli to quickly and accurately identify and "fingerprint" the bacteria. The speed of the detection process also makes it useful in detection of contaminants from potential terrorist actions.

Current tests can take days to produce results and are often limited in their ability to distinguish between various bacterial strains. But the new technology produces test results in just one to three hours, and can be operated and interpreted without highly trained personnel.

The technique was developed by Dr. Yechezkel Kashi of the Faculty of Food Engineering and Biotechnology and the Grand Water Research Institute at the Technion-Israel Institute of Technology together with Dr. Eric Hallerman of the College of Natural Resources at Virginia Polytechnic Institute and State University, and Dr. Leora Shelef of the Department of Nutrition and Food Science at Wayne State University.

"The precise identification of bacterial strains can be crucial in determining effective therapeutic strategies, and time is of the essence when it comes to certain diagnoses," Dr. Kashi said.

Dr. Hallerman said the research will improve the sensitivity, speed of detection and identification of bacteria such as E. coli. Because the test is rapid, sensitive and specific, it may be important as a microbial test of food and of water supplies to protect against terrorist attack.

In developing this detection system, the researchers found that bacterial DNA sequences contain thousands of non-coding sequence repeats, or SSRs (Simple Sequence Repeats) the so-called "junk" information contained in DNA. They found that the SSR marker sites differ in each bacterial strain, providing a unique "fingerprint" to distinguish between and identify the strains. By using existing technologies that analyse DNA sequences, Dr. Kashi's team can "fingerprint" bacteria, just as forensic experts identify suspects from fingerprints found at a crime scene.

"Potentially, we can assign each bacterium an identity card," Kashi said. "Only instead of nine digits per identity number, imagine thousands."

The technology will allow accurate, systematic comparison of bacteria across the world. Since the database will be computerized and updated, the identity card will enable the user to access all the information about the specific strain.

In addition to water, food and medical uses, Dr. Kashi's method promises to give biologists a better understanding of microorganisms. By tracking differences that accumulated slowly in bacterial genomes over time, the study of the patterns of variation among strains can lead to greater insight into bacterial evolution.

"The new 'identity card' approach will enable us to further distinguish between bacterial strains that have different virulence and clinical symptoms, for example, which strain of bacteria is likely to harm the kidney, or which strain of Streptococcus is likely to harm the heart," Dr. Kashi explained.

The next step in developing the system is to create devices that will automate the microbial DNA readings to give rapid test results at large-scale centre labs or at the doctor's office, according to Dr. Kashi.

A report on the technique was published in Genome Research last year.

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