Cattle Protozoa Help Shift Antibiotic Resistance

Agricultural Research Service (ARS) scientists in Ames, Iowa, have madeanother big finding about protozoa—single-celled predatoryorganisms—found in the gastrointestinal tract of cattle. They'vediscovered that the protozoa can facilitate the transfer of antibioticresistance from resistant bacteria to susceptible types.

Veterinary medical officerStevenCarlson at ARS' National Animal Disease Center (NADC)in Ames is the first scientist to document the role rumen protozoa play intransferring this resistance within cattle. Rumen protozoa live in the firststomach (rumen) of cattle. They engulf and destroy most bacteria.

But Carlson and colleagues have identified and described the transfer ofresistance to ceftriaxone, an antibiotic used to treat pneumonia, fromgastrointestinal tract bacteria known as Klebsiella to rumen-dwellingSalmonella that are sensitive to the antibiotic.

Last year, Carlson teamed with microbiologistMarkRasmussen—who's no longer with ARS—in a study that revealed forthe first time that disease-causing bacteria can strengthen from interactionwith protozoa that are naturally inside animals.

In that work, an antibiotic-resistant strain of Salmonella becameespecially virulent when tucked within rumen protozoa. That discovery suggeststhat naturally occurring digestive tract protozoa may be a place wheredangerous bacteria can lurk and develop.

These studies exemplify how NADC is helping to make meals worry-free forpeople who enjoy meat and poultry. Its scientists continue to break new groundin protecting consumers against Salmonella, Escherichia coli,Campylobacter and other harmful foodborne bacteria.

Cutting-edge research there includes studies on how animal diets affectdisease-causing pathogens and immunity, as well as molecular analyses ofmicrobial virulence, antibiotic resistance and host response.

Readmore about the latest work at the Ames center and other ARS researchrelated to food safety in the October 2006 issue of AgriculturalResearch magazine.

ARS is the U.S. Department ofAgriculture’s chief scientific research agency.