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Test for toxin producing molds.

Test for Toxin-Producing Molds

Not every mold is a dangerous microorganism, though the ones that produce mycotoxins assuredly are.

Kerry O'Donnell and fellow microbiologist Stephen W. Peterson are helping to keep our food free of toxin-producing molds; the ARS scientists have identified the DNA sequences of some molds that commonly produce mycotoxins in field crops.

"Molds can look very similar, even under a microscope. But we know that each species has unique DNA sequences. Through "fingerprinting" these molecular codes, we can identify specific molds and distinguish them from one another," says Peterson.

Once their fingerprints are known, researchers can design DNA probes that will quickly and accurately identify molds that produce food contaminants. He and O'Donnell are currently developing a field test that can be used by farmers and agricultural commodity graders in the field to detect Aspergillus flavus, the mold that produces aflatoxin. It is hoped this test could be ready for commercial development in a year or two.

One to two percent of the U.S. corn crop, which is valued at $20 billion annually, is lost to aflatoxin.

"With a DNA probe, a farmer could easily detect the presence of fungi that are likely to contaminate crops with aflatoxin before a large-scale problem occurs," Peterson says.

Were a probe available, farmers could decide to harvest earlier or thoroughly dry their corn right after harvest to about 12- to 14-percent moisture. "Such a practice could prevent growth of the fungi."

Current ways of checking for Aspergillus flavus are culturing methods that take up to a week to detect the mold. In contrast, a DNA probe could identify fungi in less than 24 hours. "This method is so sensitive, it can detect as few as one to three cells of the fungus," says Peterson.

Probes can also be designed for other fungi. "Most foods and feeds are susceptible to invasion by molds during some stage of production, processing, transportation, or storage," says Peterson. And some are even part of the curing (or aging) process. One such mold, Penicillium verrucosum, is used in some European cured sausages.

"It's a good fungus that helps flavor the meat. But it looks just like Penicillium veridicatum - a bad one that makes a toxic substance called ochratoxin A, associated with kidney disease," says Peterson. Another lookalike mold is Penicillium chrysogenum, which produces penicillin.

While these Penicillia molds look similar, the chemical compounds that make up their DNA are quite different. We can sequence them like letters in the alphabet to reveal their differences.
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Author:Cooke, Linda
Publication:Agricultural Research
Date:Jun 1, 1991
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