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Agricultural antibiotic use contributes to 'super-bugs' in humans

July 05, 2005

Doctors have become increasingly concerned by the problem of "super-bugs"-bacteria that have become resistant to standard antibiotics. It is well known that a high rate of antibiotic prescribing in hospitals contributes to the emergence of drug resistant bacteria. But for some antibiotics, an even more important factor contributing to such emergence, argues a team of researchers in the open access international medical journal PLoS Medicine, is the use of antibiotics in agriculture.
"Evidence suggests that antibiotic use in agriculture has contributed to antibiotic resistance in the pathogenic bacteria of humans," say David Smith of the Fogarty International Center, Jonathan Dushoff of Princeton University and the Fogarty International Center, and J.Glenn Morris Jr. of the University of Maryland.

Antibiotics and antibiotic resistant bacteria are found in the air and soil around farms, in surface and ground water, in wild animal populations, and on retail meat and poultry. These resistant bacteria are carried into the kitchen on contaminated meat and poultry where other foods are cross-contaminated because of common, unsafe handling practices. Following ingestion, bacteria occasionally survive the formidable but imperfect gastric barrier to colonize the gut-which in turn may transmit the resistant bacteria to humans.

Smith and colleagues say that the transmission of antibiotic resistant bacteria from animal to human populations is difficult to measure, as it is "the product of a very high exposure rate to potentially contaminated food, and a very low probability of transmission at a given meal." Nevertheless, based on the analysis presented in PLoS Medicine, the authors suggest that "transmission from agriculture can have a greater impact on human populations than hospital transmission."

After first Denmark and then the European Union banned the use of antibiotics for growth promotion, say the authors, the prevalence of resistant bacteria declined in farm animals, retail meat and poultry, and within the human general population. This provides evidence that antibiotic resistant bacteria can move between animals and humans.

The exact effects of agricultural antibiotic use on human health remain uncertain, they say, despite extensive investigation. "But the effects may be unknowable, unprovable, or immeasurable by the empirical standards of experimental biology." Given all of this uncertainty, Smith and colleagues suggest that adopting a "precautionary approach"-such as the European Union ban-would be suitable.

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