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Lower Prevalence of Antibiotic-resistant Enterococci On U.S. Conventional Poultry Farms That Transitioned to Organic Practices

A. R. Sapkota1*, R. M. Hutlet2, G. Zhang3, P. McDermott4, E. Kinney1, K. Schwab5 and S. W. Joseph1,6

Background: In U.S. conventional poultry production, antimicrobials are used for therapeutic, prophylactic and non-therapeutic purposes. Researchers have shown that this can select for antibiotic-resistant commensal and pathogenic bacteria on poultry farms and poultry-derived products. However, no U.S. studies have investigated on-farm changes in resistance as conventional poultry farms transition to organic practices and cease using antibiotics.

Objective: To evaluate the prevalence of antibiotic-resistant Enterococcus on U.S. conventional poultry farms that transitioned to organic practices.

Methods: Poultry litter, feed, and water samples were collected from 10 conventional and 10 newly organic poultry houses in 2008 and tested for Enterococcus. Enterococcus (n=259) was identified using the Vitek ®Compact 2 System, and tested for susceptibility to 17 antimicrobials using the Sensititre™ microbroth dilution system. Data were analyzed using SAS v9.2 and statistical associations were derived based on generalized linear mixed models.

Results: Litter, feed and water samples were Enterococcus-positive. The percentages of resistant E. faecalis and resistant E. faecium were significantly lower (p<0.05) among isolates from newly organic versus conventional houses for two (erythromycin and tylosin) and five (ciprofloxacin, gentamicin, nitrofurantoin, penicillin and tetracycline) antimicrobials, respectively. Forty-two percent of E. faecalis isolates from conventional poultry houses were multi-drug resistant (MDR) (to≥3 antimicrobial classes) compared to 10% of isolates from newly organic houses (p=0.02), and 84% of E. faecium isolates from conventional houses were MDR compared to 17% of isolates from newly organic poultry houses (p<0.001).

Conclusions: Our findings suggest that the voluntary removal of antibiotics from large-scale U.S. poultry farms that transition to organic practices is associated with a lower prevalence of antibiotic-resistant and MDR Enterococcus.

This is an open access article, click here to read more.

See a Science Daily article about this study: Poultry Farms That Go Organic Have Significantly Fewer Antibiotic-Resistant Bacteria

Environmental Health Perspectives (2011) 119: 1622-1628
DOI: 10.1289/ehp.1003350

Author Locations and Affiliations
(1) Maryland Institute for Applied Environmental Health, University of Maryland College Park, School of Public Health, MD
(2) Department of Poultry Science, Pennsylvania State University, University Park, PA
Department of Epidemiology and Biostatistics, University of Maryland College Park, School of Public Health, MD
(4) U.S. Food and Drug Administration, Center for Veterinary Medicine, Division of Animal and Food Microbiology, Laurel, MD
(5) Department of Environmental Health Sciences, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD
(6) Department of Cell Biology and Molecular Genetics, University of Marland College Park, MD
* Corresponding author, E-mail ars@umd.edu

Posted August 2011


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