Friday, July 29, 2005

New DNA Tests on Tap to I.D. Bad Microbes

Filed under: Diagnostics , Medicine

A new test from researchers at the Agricultural Research Service in Peoria, Illinois opens new diagnostic opportunities in infectious diseases:

Now, ARS scientists in Peoria, Illinois, have devised a new DNA-based approach for identifying these pathogens that's faster, easier to use, and more precise than some currently used methods.

For example, pulsed-field gel electrophoresis (PFGE) is considered the gold standard for genetically identifying L. monocytogenes bacteria that cause food poisoning. But PFGE is difficult to run, takes about 3 days, and has several disadvantages that complicate efforts to determine the relationships between different isolates.

In contrast, "Our method can be performed in a single day," says microbiologist Todd Ward, at ARS's National Center for Agricultural Utilization Research, in Peoria, "and can target single nucleotide variations within specific genes..."

On the medical front, the test may enable hospital clinicians to cast a broader net for the 30 to 40 Candida species that can cause human infections, particularly in immunocompromised people. Page says the various culture-plate testing methods now used to diagnose Candida infection are limited to a few species--notably C. albicans--and the turnaround time is 24 hours to a few weeks, delaying treatment. Genetic fingerprinting tests used in some labs may be faster, but they too detect only a few Candida species.

By comparison, the test from Kurtzman's unit identifies 32 total species--simultaneously and in less than 5 hours.

In a machine called a "flow cytometer," which can handle up to 100 samples at a time, molecules called "probes" find and bind to corresponding pieces of species-specific DNA. The researchers created the probes using DNA-sequence information from their unit's microbial-genomics database. The probes have a fluorescent marker that tells the cytometer which DNA sequence was detected. The machine clearly displays the species' identity as color-coded bar graphs.

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