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Project Overview. Antibiotic resistance continues to pose a serious threat to human health (1). Of particular concern are the agricultural effects on human health through both the consumption and production of food for the human diet. Studies suggest that agricultural and environmental reservoirs serve as potential sources of antibiotic resistance genes of clinical significance (1). Organic, grass-fed or antibiotic free labeled meat products are marketed with an implied health benefit, but are commonly contaminated with antibiotic resistant bacteria associated with foodborne illness and commensal bacteria harboring genes that confer resistance to critically important antimicrobial drugs. (1). The proposed research seeks to identify critical control points impacting maintenance and dissemination of antibiotic resistance in livestock from intensive production and grass-fed systems: 1) antibiotic use; 2) manure management; 3) soil type; 4) cover crop; 5) post-harvest practices. The aim is to move beyond only evaluating the impacts of intensive livestock production on the maintenance and dissemination of antibiotic resistant bacteria (ARBs) and antibiotic resistant genes (ARGs). But rather capture the importance of understanding the behavior of antibiotic resistance genes in the environment, including their response to agricultural practices and movement into the food supply.Project Goals and Objectives. The overall goals of this research project are to 1) identify agricultural, ecological and waste management factors that serve as critical control points for preventing the spread of antibiotic resistance from manure and lagoon effluent to livestock raised for human consumption and 2) engage in education and extension efforts related to identifying and implementing best practices that may lessen the spread of antibiotic resistance from farm to fork associated with livestock systems. Specific Objectives: Determine the effect of common therapeutic and sub-therapeutic antibiotic use practices on excretion of antibiotics and ARGs, using beef cattle and swine as models, in order to inform manure management strategies; Examine the potential for compost and swine lagoons to degrade antibiotics and attenuate ARBs and ARGs; Examine the effect of soil type on the persistence of antibiotics, ARBs, and ARGs in lagoon effluent and compost-amended soils; Quantify the transfer of antibiotics, ARBs, and ARGs to various cover crops grown in soils amended with lagoon effluent and compost; Determine the effect of waste management practices on survival and regrowth of ARBs and ARGs for different cover crops fed to livestock and develop recommendations for best practices.
Current Issue. Antibiotic resistance is recognized as a global health problem and has escalated to one of the top health challenges facing the 21st century. The relationship of drug-resistant bacteria in people to antibiotic use in food animals is still in debate. Though there is direct and indirect evidence that links antibiotic use in food animals (especially nontherapeutic use) has an impact on the health of people on farms and through the food chain. Organic, and/or grass-fed beef products make up approximately 2% of total beef sales in the United States with annual sales growth rates around 10%. Whereas conventionally raised beef cattle, which are normally started on grass but finished on higher energy grain diets. Grass-fed beef products are often marketed as safer alternatives to conventional beef products based on minimal exposure to antibiotics. However, organic production uses composted manure to fertilize crops and conventional producers use lagoon effluent to fertilize their fields used for cattle grazing. Livestock manure is an important reservoir of ARBs, ARGs (collectively known as the "resistome"), and pathogens. Recent studies suggest that there is some crop uptake of antibiotics in manure-amended soil, but at very low levels. However, there is minimal information about metabolites and how compost-soil or lagoon effluent-soil interactions influence the bioavailability of antibiotics, or selection of ARBs and ARGs. Thus the rise of ARBs and ARGs in livestock raised for human consumption may indicate a connection with the exposure and consumption of these contaminated cover crops. This project seeks to identify critical control points impacting maintenance and dissemination of antibiotic resistance in livestock from intensive production and grass-fed systems: 1) antibiotic use; 2) manure management; 3) soil type; 4) cover crop; 5) post-harvest practices of cover crops. Approach. We will determine the antibiotic and ARG excretion patterns using molecular techniques, as well as, establish the extent antibiotics are metabolize in cattle and swine. This effort will provide baseline data to determine days that manure require additional treatment because of heavy loads of antibiotics or ARGs. We will examine the potential for static and turned composting and swine lagoons to degrade antibiotics and attenuate ARBs and ARGs. This effort will provide data on whether antibiotics or ARGs are reduced and which management practice is most effective. The effect of soil type on the persistence of antibiotics, ARBs, and ARGs in compost and lagoon effluent-amended soils will be evaluated at a) microcosm-scale, b) greenhouse-scale, and c) at field-scale. This effort will provide data on how long antibiotics, ARBs, and ARGs persist in soil following land application and what soils should be avoided. Using most recent technology, quantify the transfer of antibiotics, ARBs and ARGs to various cover crops grown in soils amended with compost or lagoon effluent. This effort will provide data on which cover crops are most susceptible to contamination with antibiotics, ARBs, and ARGs and at what stage of growth is contamination the greatest. Determine the effect of post-harvest cover crop practices on ARBs and ARGs? Commercial producers/processors use different sanitizers, concentrations and contact times dependent on the fruit or vegetable, types of equipment used and the final market for the crop. However, when one considers crops used for livestock consumption, these sanitary measures aren't available. For example, when a farmer bales hay, there aren't any follow-up safety measures to minimize microbial contamination. This effort will provide data on persistence of ARBs and ARGs in such crops and serve a baseline data to establish recommendations. Ultimate Goal. The information will provide greater public awareness and those who work in agriculture and veterinary medicine will be better prepared to address antibiotic resistance associated with manure and compost management. Ultimately, the goal is to reduce the spread of antibiotic resistance, thereby reducing the number of human cases of antibiotic resistant infections.