Multidrug-resitant bacteria found to be airborne in concentrated swine operation

12/03/04

People could be exposed to antibiotic-resistant bacteria from breathing the air from concentrated swine feeding facilities, according to researchers at the Johns Hopkins Bloomberg School of Public Health. They detected bacteria resistant to at least two antibiotics in air samples collected from inside a large-scale swine operation in the Mid-Atlantic region of the United States. Until now, little research has been conducted regarding the presence of antibiotic-resistant bacteria in the air within industrial swine facilities. The study adds to the understanding of various pathways in which humans can be exposed to antibiotic-resistant bacteria, such as consumption of retail pork products and contact with or ingestion of soil, surface water and groundwater near production operations. The article is published in the online edition of Environmental Health Perspectives.

"Eating retail pork products is not the only pathway of exposure for the transfer of antibiotic-resistant bacteria from swine to humans. Environmental pathways may be equally important," said Amy Chapin, the study's lead author and a doctoral candidate at the Bloomberg School of Public Health's Department of Environmental Health Sciences.

Chapin explained that the use of antibiotics in industrial animal production has a significant impact on the emergence of antibiotic-resistant bacteria that threaten human health. Using antibiotics in animals can decrease the effectiveness of the same antibiotics used to combat human infections. The non-therapeutic use of antimicrobials in livestock production in the United States comprises an estimated 60 to 80 percent of the total antimicrobial production nationally. Non-therapeutic doses of drugs are given to swine to promote growth and improve feed efficiency - not to treat actual swine disease.

The airborne bacteria samples that were found to be multidrug-resistant were: Enterococcus, coagulase negative staphylococci and viridans group streptococci. These bacteria are associated with a variety of human infections. The study found that 98 percent of the isolated samples were resistant to at least two of the following antibiotics: erythromycin, clindamycin, virginiamycin and tetracycline. All of these drugs (or their human drug counterparts) are important antibiotics in the treatment of human infections. In contrast, none of the bacterial samples were resistant to vancomycin – an antibiotic that has never been approved for use in swine production in the United States.

The researchers believe workers at concentrated animal feeding operations are at greatest risk for airborne exposure to antibiotic-resistant bacteria. However, the same workers may also become reservoirs of drug-resistant bacteria that can be spread to family and the broader community. The study also raises questions about the spread of drug-resistant bacteria to areas beyond the immediate site through ventilation fans and by the application of manure from feeding operations to off-site fields.

"These research findings add another piece to our understanding of human exposure to antibiotic-resistant bacteria," said Kellogg Schwab, PhD, assistant professor in the Bloomberg School of Public Health's Department of Environmental Health Sciences and the study's corresponding author. "Finding and documenting the multiple environmental pathways of exposure are critical to finding solutions to the growing, serious problem of antibiotic-resistant bacteria in humans."

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