Antimicrobial protein protects against mastitis-causing bacteria.

A USDA-ARS-led team has combined specific DNA segments from two different sources to produce a novel antimicrobial protein. The resulting fusion antimicrobial protein degrades the cell walls of several bacterial pathogens in a solution of whey extracted from cow's milk.

The technology is a key step to giving dairy cows a built-in defense against mastitis, a disease that costs U.S. dairy producers up to $2 billion annually. In the realm of infectious disease, one way to reduce microbial resistance that results from widespread antibiotic use is to come up with new ways to fight pathogens. The findings from this experimental study were published in the April 2006 issue of Applied Environmental Microbiology.

David Donovan, a USDA-ARS molecular biologist, presented the study's results at the American Society for Microbiology's 2006 annual meeting in Orlando, FL. Donovan is the inventor on a USDA-ARS-filed patent application that describes the technology behind fusing the protein-coding DNA sequences that produce the novel fusion antimicrobial. The investigators hope to use the technology to produce fusion proteins as alternatives to broad-range antibiotics, both in clinics and on farms. Milk containing the fusion protein would first require safety testing and regulatory approval.

Researchers are testing the constructs in whole milk to predict their activity in the mammary gland. However, regardless of their activity in milk, the constructs are active against both streptococci and S. aureus, so they should also have clinical applications. The scientists would need to work with a commercial organization to stabilize the proteins in a micelle or other delivery mechanism.

Bacteria have layers of macromolecules that provide strength and shape to their cell walls. The fusion antimicrobial protein, as a cell wall-degrading enzyme, kills pathogens by decomposing this structural layer and causing the cell to break down. The B30-lysostaphin fusion protein developed by the research team is active against both S. aureus and three streptococcal mastitis pathogens that together are responsible for up to 50% of the dairy cattle mastitis that occurs in the United States.

Mastitis is the inflammation of the mammary gland caused by microorganisms that invade the udder, multiply and produce toxins that are harmful to the mammary gland. Up to 95% of mastitis problems are caused by microorganisms invading the mammary gland via the teat end. Factors contributing to mastitis include people, milking equipment, weather, housing conditions (bedding and ventilation), other diseases and metabolic disorders, milking procedures, and contaminated drugs, teat dips, water and treatment equipment.

Further information. David Donovan, USDA-ARS Biotechnology and Germplasm Laboratory, Beltsville Agricultural Research Center-EAST, Building 200, Room 104, Beltsville, MD 20705; phone: [phone]; fax: [phone]; email: [e-mail].