A TIGER to track pathogens
TIGER, short for "Triangulation Identification for Genetic Evaluation of Risks," is a tool used by several U.S. labs which need to quickly identify pathogens, such as bacteria, fungi, and other microorganisms that cause disease. In TIGER Technique Targets Plant Pathogens, the USDA/Agricultural Research Service (ARS) says that this detection tool is the only one that provides at the same time speed, accuracy, sensitivity, and ease of use. It can be used to protect America's crops from diseases caused by pathogens brought to the U.S. by tourists -- or terrorists. TIGER is also used by the U.S. Army to detect human pathogens which could be employed against troops deployed abroad or in the U.S. by bioterrorists.
So what is TIGER? Here is the answer from the Agricultural Research Service (ARS).
Developed by Ibis Biosciences of Carlsbad, California, [a subsidiary of Isis Pharmaceuticals, Inc.,] in collaboration with Science Applications International Corporation, of San Diego [(SAIC)], TIGER can be used to identify virtually every microbe in a given sample -- of soil, water, air, blood, plant, or otherwise. Furthermore, TIGER can identify microbes in minutes. Other methods, including some PCR-based ones [PCR meaning "polymerase chain reaction"], take hours, days, or even weeks, and they typically detect only a few, to a few dozen, pathogens at a time.
As you can see below, the bacterial landscape to check is quite large, so TIGER has plenty of things to track (Credit: Ibis Biosciences).
And below is a slide showing what kinds of problems can be addressed by TIGER (Credit: Ibis Biosciences).
Here is how TIGER works.
Like other PCR-based fingerprinting methods now used for early detection and routine monitoring of plant pathogens, TIGER makes use of specially designed fragments of nucleic acid called "primers." Their job is to find, and bind to, complementary segments of DNA in a pathogen’s genome -- if it’s indeed present in a sample.
One drawback to today’s PCR methods is that the nucleic acids making up the targeted pathogen's DNA must first have been sequenced. But TIGER's primers are very general, and they seek to bind with genes or gene regions shared among all bacterial species. Because of this, TIGER's primers serve as a one-size-fits-all tool that detects all bacteria in a given sample. Most importantly, it skips the need for prior genome sequencing.
But TIGER is not only used to ensure farmland security. It is also used by the U.S. Army. The U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID) has been using TIGER since 2005 "as part of the military lab’s efforts to detect, diagnose, and counter human pathogens -- whether encountered by troops deployed abroad or released domestically as bioterrorist attack agents."
For more information about TIGER, you should read a presentation given by Dr. Lawrence Blyn from Isis Pharmaceuticals at the 1st Annual Food Protection and Defense Research Conference which was held on November 2-4, 2005 in Atlanta, GA. Here are two links to the Conference Papers and to Blyn's paper, "The TIGER Biosensor: Rapid Broad Range Pathogen Detection in Diagnostics and Food Protection" (PDF format, 45 pages, 3.75 MB). You can see larger versions of the images above on pages 5 and 15.
A last word: I didn't pay attention to this information in November. Fortunately, Science Daily chose to publish yesterday an adaptation of the ARS news release under a catchy title, "Scientists Leverage Robotic Diagnostic Technology To Diagnose Plant Diseases."
Sources: USDA/Agricultural Research Service, November 3, 2006; and various otherwebsites
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