Studies to pinpoint how, when resistance spreads

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Genetic analysis could help identify how drug resistance spreads among bacteria and what humans can do to reduce that spread.

Microbiologists with the Department of Agriculture's Agricultural Research Service have developed methods to detect more than 700 genes found in pathogens such as Salmonella spp and Escherichia coli and connected with resistance to one or more antimicrobials. Studies published in 2010 include examinations of Salmonella Newport in dairy cattle, Salmonella Javiana in humans, and E coli in chicken.

"We're hoping that our research will have an impact on understanding what is causing multidrug resistance and what is causing its spread," said Jonathan G. Frye, PhD, a microbiologist for the USDA ARS.

Dr. Frye has studied genes connected with antimicrobial resistance since he was hired by the agency in 2003, and the development of DNA microarray techniques to find those genes is the fruition of his work. He and collaborators published a proof-of-concept paper on the technique in 2006.

Dr. Frye is among researchers with the ARS and the Sidney Kimmel Cancer Center in San Diego who searched GenBank, a database administered by the National Center for Biotechnology with the National Institutes of Health, for information on published genetic sequences connected with antimicrobial resistance. That information was used to design nucleotide probes capable of detecting those genes.

Dr. Frye said the development can help to identify how genes connected with resistance are spread among bacteria and factors that amplify or select for resistance in various environments and within animals. A long-term goal of his studies is to find points during animal production when antimicrobial-resistant bacteria are more prevalent in the animals and in their environments.

Although he does not perform clinical work, Dr. Frye said some researchers in academia are developing clinical assays to use for diagnosis and tailored treatment of antimicrobial-resistant disease in animals and people.

Genetic links to resistance recently gained increased attention owing to publications about a gene identified as NDM-1, which has been associated with multidrug-resistant bacterial infections in humans. Dr. Frye said he had begun work on developing a probe for the gene, and he and colleagues at Walter Reed Army Institute of Research will collaborate on research into the gene.

The World Health Organisation, citing an article in Lancet Infectious Diseases about NDM-1, released a statement Aug. 20 that urges countries to be ready to implement hospital infection control measures and reinforce national policies on prudent antimicrobial use.

"While multidrug-resistant bacteria are not new and will continue to appear, this development requires monitoring and further study to understand the extent and modes of transmission, and to define the most effective measures for control," WHO information states.

Check out reports, policies, and guides on antimicrobial use and antimicrobial resistance here.