| The goal of my dissertation research was to characterize potential environmental pathways of exposure to antimicrobial resistant bacteria and resistance genes associated with waste from industrial poultry production and present evidence on the need for improved food animal waste management as it relates to public health.; More than 10 million metric tons of untreated poultry litter (i.e., excreta, feathers, spilled feed, bedding material, soil and dead birds) is applied to land every year in relatively small geographic regions of the United States, and production trends indicate that this practice will continue to grow. To date, most research has focused on potential ecological impacts of land application of animal waste associated with nutrient overloading of aquatic systems. In addition to nutrients, however, this waste also contains animal feed constituents, such as antimicrobials, and antimicrobial resistant strains of pathogenic and non-pathogenic bacteria.; The development of antimicrobial resistant bacteria has been strongly associated with the use of antimicrobials for promoting growth, improving feed conversion efficiency and preventing disease in poultry flocks. Further, it is well documented that the use of antimicrobials in poultry production is associated with increased risks of foodborne infections, including infections by resistant pathogens. There is a paucity of information, however, on the spread of antimicrobial resistant bacteria as well as genetic determinants conferring resistance in the environment through the extensive practice of land application of animal wastes, or additionally dissemination of resistance by other means.; In my first study (Chapter 2),1 assessed typical poultry litter handling methods and describe factors (e.g. pH, temperature, time, and moisture) that affect the survival of drug-resistant enterococci and staphylococci. I also identified resistance genes in isolates from the litter stored over a period of 120 days. Although elevated temperatures greater than 60°C were observed in the core of the litter piles, both antimicrobial resistant enterococci and staphylococci, as well as resistance genes, persisted throughout the 120 day study period. Resistance genes identified in the study include: erm(B), erm(A), msr(A/B), msr(C), erm(A), vat(E) and erm(C). This study indicates that typical storage practices of poultry litter are insufficient for reducing drug resistant enterococci and staphylococci.; Chapter 3 is a study of antimicrobial resistant bacteria and resistance genes isolated from flies in the poultry production environment, a potential pathway of human exposure to resistant bacteria. Chapter 3 also combines data from Chapter 2 to show the correlation of resistance patterns and resistance genes found in enterococci and staphylococci from flies to resistance patterns and genes found in enterococci and staphylococci from poultry litter. The observed patterns of resistance and resistance genes indicate that flies around poultry confinement operations likely transmit antibiotic resistant enterococci and staphylococci to the surrounding community. Resistance genes erm(B), msr(C), msr(AIB) and genetic mobile elements associated with Tn916, were found in isolates recovered from both poultry litter and flies.; In Chapter 4, I reviewed public health risks associated with waste generated from industrial food animal operations and present a number of policy recommendations for improving waste management. Finally, in Chapter 5, I describe the limitations of biosecurity and biocontainment measures at CAFOs and present the public health risks, such as avian influenza, associated with the industrialized model of raising poultry. As an addendum, I provide an analysis (Appendix A) evaluating the economic effects associated with discontinuing the use of antimicrobials for growth promotion in broiler chicken production. |
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