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Subtherapeutic Antibiotics May Decrease E. coli 0157:H7 Shedding

Subtherapeutic Antibiotics May Decrease E. coli 0157:H7 Shedding

Nancy Cornick, Iowa State University associate professor of veterinary microbiology, has found that some antibiotics given at subtherapeutic levels may be helpful in reducing the pathogen E. coli 0157:H7 in swine.

In her study, Cornick examined the usage of three antibiotics – tylosin, chlortetracycline and bacitracin – that are commonly used at dosages for growth promotion.

Pigs that were fed the diet supplemented with chlortetracycline and tylosin shed significantly less E. coli 0157:H7 than pigs fed antibiotic-free diets, according to Cornick’s research project.

“The antibiotics I chose were the ones that were most commonly added at subtherapeutic doses, which is what they’re usually looking for with growth promotion,” she adds.

Cornick notes that many scientists favor an end to administering subtherapeutic antibiotics because they aren’t used for disease treatment or disease prevention.

E. coli 0157:H7 is well known as a major cause of food-borne illness in meat that comes from cattle. In recent years, reports have linked pork products to outbreaks of human disease. Cornick says those cases are rare, but the potential problem should be on pork producers’ radar.

A case in point occurred in California, where feral pigs were suspected along with cattle of contributing to E. coli 0157:H7 contamination of a vegetable field in the Salinas Valley in 2006.

“I would argue that those feral pigs were probably exposed to fewer antibiotics than conventionally raised swine,” Cornick points out. “That may be a reason that they were colonized by the E. coli 0157:H7.”

Since E. coli 0157:H7 is not commonly recovered from pigs, the potential makes it worth investigating. Experimentally challenged animals have been shown to transmit the pathogen even with very low levels of fecal shedding.

If antibiotic use tapers off, Cornick theorizes there could be a corresponding increase of E. coli 0157:H7 in swine.

“Maybe there would be,” she says, “or if I can find another reason why E. coli 0157:H7 isn’t in swine, then maybe that’s something cattle producers can use as a management strategy.”

A summary of Cornick’s research report appeared recently in the winter 2010 edition of The Food Safety Consortium Newsletter. The newsletter is a production of the member schools of the consortium: University of Arkansas, Iowa State University and Kansas State University. Visit

The scientific article detailing her work can be found at[Jour]+AND+2009[pdat]+AND+Cornick[author].