Transgenic Cows Resist Mastitis-Causing Bacteria

WASHINGTON, April 4--U.S. Department of Agriculture researchers have used gene-transfer technologies to produce dairy cows that resist a widespread bacterial infection called mastitis.

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

This scientific discovery, published in the current edition of Nature Biotechnology, demonstrates the potential of biotechnology for developing cattle with resistance to mastitis. Currently, vaccines, antibiotics and a cow's own immune system cannot effectively fight the bacterium Staphylococcus aureus, a major cause of mastitis.

A scientific team led by Robert J. Wall, an animal physiologist with the ARS Biotechnology and Germplasm Laboratory in Beltsville, Md., built a transgene--genetic material produced using recombinant DNA technology--that includes the genetic code for producing a naturally occurring, antimicrobial protein called lysostaphin.

While all milk contains several naturally occurring antimicrobial proteins, such as lysozyme and lactoferrin, none of the milk produced by the three cows in this research effort will be consumed. Use of milk containing lysostaphin would require federal regulatory approval after rigorous food safety testing. This effort is at the early stages of research and development.

The research shows that the gene for secreting lysostaphin comes from a non-pathogenic species of Staphylococcus that uses the protein to repel its cousin, S. aureus. The scientists introduced this transgene into Jersey cows. The lysostaphin is secreted into milk, where it kills S. aureus, thus protecting cows from becoming infected.

"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," said Wall. 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."

Overall, the researchers found that in tests, 71 percent of the mammary glands that were exposed to S. aureus from nontransgenic animals became infected--compared to only 14 percent for the transgenic animals.

Future studies will include developing similar defenses against other pathogens that affect dairy cattle, as well as gauging the milk's ability to effectively produce common dairy products, such as cheese and yogurt.