DNA Chips Spot and Help Track Antibiotic Resistance

A DNA chip, or DNA microarray, is a small glass slide that can reveal the presence or absence of particular DNA sequences in a sample. This tool has allowed clinicians to test for genetic mutations and diseases in people.

Now, ARS microbiologists Jonathan Frye, Charlene Jackson, Mark Englen, and Paula Cray have developed a DNA microarray that detects more than 100 antimicrobial-resistance genes in many types of bacteria.

Antimicrobial compounds, or antibiotics, have been used for years to fight bacterial infections. But some bacterial pathogens, like Salmonella, Escherichiacoli, Campylobacter, and Enterococcus, are becoming resistant to more antibiotics. Scientists need to know which bacteria are resistant to which antibiotics and how the bacteria continue to develop resistance to other ones.

“We use DNA chips to detect genes that make bacteria resistant to antibiotics,” says Frye. “Unfortunately, DNA that confers resistance can sometimes be exchanged when a lot of bacteria are together. Some exchanges are random, some are programmed, and some are brought on by stresses in the environment.”

Frye and associates in the Bacterial Epidemiology and Antimicrobial Resistance Unit in Athens, Georgia, also use microarray technology to track resistant bacteria in samples collected from animals on the farm or in slaughter facilities. “This information will help identify possible targets for intervention strategies to prevent development and transfer of bacterial resistance,” says Frye.

“The great thing about DNA microarrays is that we can search for many genes at once in any particular sample,” he says. “Before, we had to put bacteria in a growth media laced with antibiotics. The bacteria that grew were resistant to that antibiotic. Then we’d search for the gene or genes responsible for the resistance. But now we’ll know which genes could be responsible if they are expressed, because they’ll show up on the DNA microarray.

“If you identify the source of resistance genes in bacteria, then you can begin tracking where the resistance is coming from and develop an intervention strategy. Sources of resistant bacteria could be soil, other animals, or even humans who handle the animals on the farm. The DNA microarray gives us a place to start.”—By Sharon Durham, Agricultural Research Service Information Staff.

Jonathan Frye is with the USDA-ARS Richard B. Russell Agricultural Research Center, Bacterial Epidemiology and Antimicrobial Resistance Unit, 950 College Station Rd., Athens, GA 30605; phone (706) 546-3677, fax (706) 546-3066.

"DNA Chips Spot and Help Track Antibiotic Resistance" was published in the November 2005 issue of Agricultural Research magazine.