Agriculture Antibiotics and Human Resistance

US - While experts agree that antibiotic overuse is one of the key contributors to the recent rise in drug-resistant infections, research is raising the prospect that agricultural use is also having a detrimental effect on human health.
calendar icon 16 March 2009
clock icon 3 minute read

Speaking 24 February at a Capitol Hill briefing co-organized by AAAS, three top experts warned that the increased use of antibiotics in agricultural feed contributes to drug-resistant infections in humans. But just how extensive that relationship is has yet to be determined.

David Wallinga, director of the Food and Health Program at the Institute for Agriculture and Trade Policy, said that stockyard conditions are breeding grounds for antibiotic-resistant infections that can be transmitted to the general population through the food we eat, interactions with agricultural workers, or groundwater and soil from the farms.

"agricultural settings are a reservoir of resistance with a potential to spread dangerous bacteria to the larger community"
Tara Smith, assistant professor of epidemiology at the University of Iowa

"There is a scientific consensus that antibiotics used in agriculture do contribute to rising resistance transmitted to humans," said Wallinga. And, he predicted, that may mean a proliferation of untreatable infections driving up healthcare costs.

Joanne Carney, director of the AAAS Center for Science, Technology, and Congress, said that the briefing was timely due to legislation expected to be reintroduced in the Senate later this year. The bill would phase out some agricultural antibiotic use over two years and require pharmaceutical companies to document the type and quantity of drugs they sell to livestock feed producers.

"With healthcare reform a high priority for the White House and Congress, it is important for policymakers to better understand the science behind antimicrobial resistance in agriculture and its impact to public health," said Carney.

Tara Smith, assistant professor of epidemiology at the University of Iowa, said that while everyone should be concerned about the potential spread of antibiotic-resistant bacteria, Iowa is especially vulnerable due to her state's livestock population and economic dependence on agriculture. The state's 3 million residents co-exist with 92 million farm animals—19 million swine, 65 million chickens, 4 million turkeys, and 4 million cows. In addition, Iowa is the county's leading producer of pork and eggs.

Smith outlined a study published last month in the Public Library of Science in which she led a team surveying swine and agricultural workers to see if they carried antibiotic-resistant bacteria.

The team traveled to seven farms throughout Iowa that comprised a closed farming system—the complete agricultural process from the hog's birth to slaughter—and swabbed the nasal passages of the animals and human workers. Of the 209 nasal swabs obtained from pigs, 70% showed Methicillin-resistant S. aureus (MRSA) bacteria.

In addition, 64% of workers from the farm system tested positive for MRSA. After analyzing the bacteria, the team found that the bacteria were genetically similar, suggesting that there was transmission between humans and animals.

"Due to thousands of animals being confined to a small space, agricultural settings are a reservoir of resistance with a potential to spread dangerous bacteria to the larger community," said Smith. She said that 18,000 deaths and 94,000 infections were attributed to MRSA in 2005.

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