WASHINGTON — Either one of two forms of a vaccine recently developed by Agricultural Research Service scientists might help to reduce the spread of E. coli O157:H7 bacteria via immunizing calves, according to ARS staffer Marcia Wood.

Although the microbe can flourish in the animals' digestive tracts and doesn't cause them to show clinical symptoms of illness, E. coli can cause bouts of diarrhea and, sometimes, life-threatening hemolytic uremic syndrome in humans.

The novel vaccines were developed by research microbiologists Vijay K. Sharma and Thomas A. Casey in their laboratories at the agency's National Animal Disease Center in Ames, Iowa. A patent is currently being sought for it.

Preventing E. coli O157:H7 from proliferating inside cattle helps to limit contamination of meat at the packinghouse, and reduces shedding of the microbe into the animals' manure. Manure-borne E. coli can be moved by rainfall into drinking water. It can also end up in irrigation water, and can contaminate fruits, vegetables or other crops, increasing the risk of an outbreak of foodborne illness.

Ms. Wood writes one form of the vaccine is made up of cells of a strain of E. coli O157:H7 that is lacking a gene known as hha. A second form of the vaccine contains an E. coli strain lacking hha and a second gene, sepB. In either vaccine, the E. coli strain produces a large quantity of immunogenic proteins, which trigger the immune system response that prevents E. coli O157:H7 from successfully colonizing cattle intestines.

Holstein calves were immunized in preliminary tests at three months of age with a placebo or either form of the vaccine. Six weeks later, the animals were given a dose of E. coli O157:H7, and, for the next 18 days their manure was tested for evidence of the microbe. Researchers found that calves receiving either vaccine had reduced or non-detectable levels of E. coli in their manure within only a few days after being inoculated with the bacteria.