Johns Hopkins Gazette | March 23, 2009
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The newspaper of The Johns Hopkins University March 23, 2009 | Vol. 38 No. 27
 
Flies May Spread Drug-Resistant Bacteria From Poultry Operations

By Tim Parsons
School of Public Health

Researchers at the Johns Hopkins Bloomberg School of Public Health have found evidence that houseflies collected near broiler poultry operations may contribute to the dispersion of drug-resistant bacteria and thus may increase the potential for human exposure to drug-resistant bacteria.

The findings demonstrate another potential link between industrial food animal production and exposures to antibiotic-resistant pathogens. Previous studies have linked antibiotic use in poultry production to antibiotic-resistant bacteria in farm workers, consumer poultry products and the environment surrounding confined poultry operations, as well as to releases from poultry transport.

"Flies are well-known vectors of disease and have been implicated in the spread of various viral and bacterial infections affecting humans, including enteric fever, cholera, salmonellosis, campylobacteriosis and shigellosis," said lead author Jay Graham, who conducted the study as a research fellow with the Bloomberg School's Center for a Livable Future. "Our study found similarities in the antibiotic-resistant bacteria in both the flies and poultry litter we sampled. The evidence is another example of the risks associated with the inadequate treatment of animal wastes."

Added Ellen Silbergeld, senior author of the study and professor in the Bloomberg School's Department of Environmental Health Sciences, "Although we did not directly quantify the contribution of flies to human exposure, our results suggest that flies in intensive production areas could efficiently spread resistant organisms over large distances."

Graham and his colleagues collected flies and samples of poultry litter from poultry houses along the Delmarva Peninsula, a coastal region shared by Maryland, Delaware and Virginia that has one of the highest densities of broiler chickens per acre in the United States. The analysis by the research team isolated antibiotic-resistant enterococci and staphylococci bacteria from both flies and litter. The bacteria isolated from flies had very similar resistance characteristics and resistance genes to bacteria found in the poultry litter.

Flies have ready access to both stored poultry waste and to poultry houses. A study by researchers in Denmark estimated that as many as 30,000 flies could enter a poultry house over the course of a six-week period.

Additional authors of the study are Lance Price, Sean Evans and Thaddeaus Graczyk. The study is published in the April issue of Science of the Total Environment. The research was funded by a grant from the Johns Hopkins Center for a Livable Future.

According to Robert Lawrence, director of the Center for a Livable Future, confined animal feeding operations — where thousands of animals are crowded together and are fed antibiotics for growth promotion — create the perfect environment for selection of bacteria that are resistant to antibiotics. "Antimicrobials are among the most important developments of the 20th century in managing infectious diseases in people. We can't afford to squander them by using them as growth promoters in industrial food animal production," Lawrence said. "The increase in antibiotic-resistant bacteria is a major threat to the health of the public, and policy-makers should quickly phase out and ban the use of antimicrobials for nontherapeutic use in food animal production."

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