Researchers detect antibiotic-resistant genes

by Bryan Salvage
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WASHINGTON — For the first time, more than 700 genes that give microbes such as Salmonella and E. coli the ability to resist antibiotics and other antimicrobial compounds have been detected by researchers with the U.S. Department of Agriculture’s Agricultural Research Service. The findings were the result of scientists and cooperators using an advanced genetic screening technique, writes the agency’s Sharon Durham.

Researchers used DNA microarray technology to find the resistance genes in a wide variety of bacteria such as Salmonella, E. coli, Campylobacter, Listeria, and Enterococcus, among others. All of these organisms can cause food poisoning and are thus a major public health concern. Worries exist amongst the researchers that some of these organisms may have acquired genetic resistance to the antibiotics used to kill them. One important step for scientists looking for new ways to control these organisms is finding the genes that confer resistance.

All genes identified in organisms are logged into GenBank, a gene database administered by the National Center for Biotechnology Information at the National Institutes of Health. A.R.S. microbiologists Jonathon Frye, Rebecca Lindsey, Charlene Jackson, Paula Fedorka-Cray, Mark Berrang, Mark Englen and Richard Meinersmann at the agency's Bacterial Epidemiology and Antimicobial Resistance Research Unit in Athens, Ga., along with collaborators at the Sidney Kimmel Cancer Center in San Diego, Calif., searched through GenBank for genes annotated by other scientists to likely encode resistance.

About 1,000 unique genes from among 5,000 genes found in GenBank that included the words "antimicrobial resistance" in their description were selected by Mr. Frye and his colleagues. They then designed a microarray of more than 700 DNA probes to detect the resistance genes. A DNA microarray is a small glass slide used to test genetic samples for the presence of specific genes, Ms. Durham explains.

Pieces of DNA called probes are designed to detect the genes that are known to confer antimicrobial resistance in order to make the arrays. These probes are then fused onto the glass slides in specific configurations.

DNA extracted from the bacterium to be tested is tagged with fluorescent dyes and then put into contact with the slide containing the probes to use the array. The antimicrobial-resistance genes in the bacteria will then attach themselves to the probes they match on the slide, making the specific probe for that gene fluoresce and thus identifying the antimicrobial resistance gene that was in the bacterium.

This work was published in the scientific journal Microbial Drug Resistance.
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