Genetically engineered cows resist bacteria that cause mastitis

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Researchers at the Department of Agriculture have genetically engineered dairy cows that resist mastitis caused by a widespread bacterium. The scientific advancement, published in the April issue of the journal Nature Biotechnology, demonstrates the potential for biotechnology to be used to battle a disease.

"This research is an important first step in understanding how genes can be used to protect animals from disease," said Edward B. Knipling, PhD, administrator of the USDA Agricultural Research Service.

Because vaccines, antimicrobials, and a cow's immune system cannot effectively fight Staphylococcus aureus, a major cause of mastitis, scientists led by Robert J. Wall, PhD, set out to investigate new ways of battling the disease. Dr. Wall is an animal physiologist with the ARS Biotechnology and Germplasm Laboratory in Beltsville, Md.

Using gene-transfer technology, the researchers produced several Jersey cows with a gene that allows the cows to produce lysostaphin in their milk. Lysostaphin is a naturally occurring antimicrobial protein. The gene was taken from a nonpathogenic species of Staphylococcus that uses the protein to repel its cousin, S aureus.

"The three genetically engineered cows that have been tested so far are expressing lysostaphin in their milk and are resistant to S aureus intramammary infection," Dr. Wall said. "All three transgenic cows showed little or no sign of infection after repeated exposures to S aureus, and one, named GEM, never became infected, indicating complete protection."

In tests, 71 percent of the mammary glands that were exposed to S aureus from nontransgenic animals became infected, compared with only 14 percent for the transgenic animals. The researchers next plan to gauge the milk's ability to effectively produce common dairy products, such as cheese and yogurt.

While milk contains several naturally occurring antimicrobial proteins, such as lactoferrin, the sale of milk containing lysostaphin would require federal regulatory approval after rigorous food safety testing. To date, the Food and Drug Administration has not granted approval for any products from transgenic animals to enter the food supply, according to Linda Grassie, a spokesperson for the FDA.