Researchers Cite Link Between Sub-Therapeutic Antibiotic Dosing In Livestock And Antibiotic Resistance In Humans, Call For Regulation

FAYETTEVILLE, Ark. - A University of Arkansas law professor and a graduate student in biochemistry call for regulation of the use of millions of tons of antibiotics in livestock, citing their contribution to the growing problem of antibiotic resistant infections that plague humans.

Carol Goforth, Clayton N. Little Professor of Law, and Robyn Goforth, a biochemistry graduate student, present their findings in the paper "Appropriate Regulation of Antibiotics in Livestock Feed" in the current issue of the Boston College Environmental Affairs Law Review.

The Goforths cited a growing body of scientific literature that links sub-therapeutic doses of antibiotics in livestock to mutated, antibiotic-resistant bacteria, and then to outbreaks of antibiotic resistant infections in humans.

"Once you get the pool of resistance out there it’s difficult to stop its spread," Robyn Goforth said.

Farmers feed animals sub-therapeutic doses of antibiotics to prevent diseases in crowded conditions and to promote animal growth. Theoretically, the antibiotics will kill disease-causing bacteria that the animals harbor.

However, bacteria often contain slight mutations in their genetic make-up that allow them to escape death. These bacteria, resistant to the antibiotic, can then multiply and can quickly become the dominant strain. One E. coli bacterium, for instance, can produce more than a million progeny in seven hours - a quickly growing problem if an antibiotic resistant organism infects a person.

Just because a bacteria strain only infects chickens doesn’t mean antibiotic resistance will remain within the chicken population. Resistance can spread from bacteria that infect livestock to those that infect humans.

"Bacteria are amazing in their ability to pass resistance to other species of bacteria," Robyn Goforth said. These tiny organisms often contain small pieces of DNA, called plasmids, that they can transfer to other bacteria, with resistance mutations embedded within the plasmid’s genetic code.

Many drugs used to treat humans also end up in livestock feed - amoxicillin, ampicillin, erythromycin, neomycin, penicillin and tetracycline are among the most common drugs used for treating both people and farm animals.

Although many scientists have written articles on the problem of antibiotic resistance in humans and its possible link to antibiotic use in livestock feed, the legal profession has remained relatively silent on the issue, Carol Goforth said.

"Addressing this subject requires the evaluation of lots of scientific data. That may be why there’s nothing in the legal literature," she said.

The researchers make four recommendations:

1. No new antibiotics should be approved for agricultural use unless the drug sponsor can provide convincing evidence that the use of the drug in this manner presents no appreciable risk to human health.
2. Sub-therapeutic use of antibiotics in farm animals should be phased out as rapidly as possible, unless the drug sponsor can provide convincing evidence that the use of the antibiotic in question presents no appreciable risk to human health.
3. Agricultural use of antibiotics should be limited to short-term use under the care of a licensed veterinarian unless the drug sponsor can show that the antibiotic in question is not used in human populations, is not medically related to such drugs and does not select for multi-drug resistance in bacteria.
4. Information about alternatives to the use of antibiotics to maintain livestock health and growth rates should be developed and disseminated among the agricultural and veterinary community.

"This puts the burden of proof on the drug companies to show that the use of antibiotics in agriculture will not cause harm in humans," Carol Goforth said.

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