DNA-Spotted Microarray Developed to Detect Bioterror Pathogens

Lethal diseases frequently spread faster than it takes to diagnose them in the laboratory. To correct that, researchers have developed a test to bring that time from days down to hours.

Dr. Sanjeev Narayanan, assistant professor, and Dr. Greg Peterson, research microbiologist, both from the department of diagnostic medicine and path biology at Kansas State University (Manhattan, KS, USA), are using a device called a DNA-spotted microarray to pinpoint the specific genetic markers that distinguish one pathogen apart from another and determine antibiotic resistance.

Traditionally, it takes days and multiple lab workers to screen a sample of soil, water, or feces for just one pathogen. Additional time is then needed to look for resistance to antibiotics. The new test developed at Kansas State simultaneously looks for multiple diseases and antibiotic resistance, reducing the time it takes from sampling to diagnosis to about 24 hours. "We needed a mass, high through-put system,” Dr. Narayanan noted. "The longer a serious disease goes undiagnosed, the harder it is to treat, and the further it can spread.”

The researchers analyzed DNA of hundreds of pathogens and synthesized DNA probes for the specific genetic sequences that set each pathogen apart. Up to now, they can detect as many as 557 genes, making it possible for them to screen for 40 different species of bacteria, 1,200 serotypes of Salmonella, five common serotypes of Escherichia coli, and resistance to the 45 most common antibiotics used to treat human and animal illnesses caused by these pathogens.

When a sample is submitted, technicians extract and fluorescently label total DNA, and run a microarray to find out whether a particular gene is present. According to Dr. Narayanan, the next phase will be to develop a test that indicates how much of a pathogen is present.

Dr. Narayanan commented that he and Dr. Peterson developed the test because most human and animal infections are caused by a combination of pathogens. Under the current practice, it can take days to isolate and identify each individual pathogen and generate their antimicrobial resistance profiles. This means physicians and veterinarians often initiate antibiotic treatment before knowing precisely what the actual problem is.

"This new test will eliminate a lot of the guesswork,” Dr. Narayanan said. It will inform the doctor how many different kinds of pathogens are in a sample and which antibiotics would not work, all in a shorter time frame. The test's efficiencies also translate into lower cost, he reported.

Should the United States ever be attacked with biologic weapons the new test also would help in quickly identifying all of the bacterial pathogens used. "Being able to get such quick results for so many pathogens at once will become critical in case of bioterrorism,” Dr. Narayanan said. "Under that scenario, every minute counts in providing treatment or preventing disease spread.” Moreover, such pathogens would likely be engineered for resistance to common drug treatment, and the new test would determine such resistance rapidly, Dr. Narayanan reported.

The test is currently being used in research labs at Kansas State's College of veterinary medicine to detect animal and zoonotic pathogens; zoonotic pathogens can be transmitted between humans and animals. The test also is being used to track the flow of genetic elements in food production systems, such as feedlots. However, Dr. Narayanan hopes the test could soon be used to enhance the clinical diagnosis of animal and human infections.

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