Ag Research Service (ARS) scientists have discovered that protozoa -- single-celled predatory organisms -- found in the gastrointestinal (GI) tract of cattle can facilitate the transfer of antibiotic resistance from resistant bacteria to susceptible types.

Veterinary medical officer Steven Carlson at the National Animal Disease Center (NADC) in Ames, IA, is the first scientist to document rumen protozoa's role in transferring resistance within cattle.

Rumen protozoa engulf and destroy most bacteria. But Carlson and colleagues have ID'd and described the transfer of resistance to ceftriaxone, an antibiotic used to treat pneumonia, from GI tract bacteria known as Klebsiella to rumen-dwelling Salmonella sensitive to the antibiotic.

Last year, Carlson teamed with former ARS microbiologist Mark Rasmussen in a study revealing that disease-causing bacteria can strengthen from interaction with protozoa that are naturally inside animals. In that work, an antibiotic-resistant strain of Salmonella became especially virulent when tucked within rumen protozoa. The discovery suggests naturally occurring digestive-tract protozoa may be a place where dangerous bacteria can lurk and develop. To read more, visit www.ars.usda.gov/is/pr/2006/061003.htm.
-- Clint Peck