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Use it and lose it: The dilemma of antibiotic resistance development
Amid concerns that the loss of antibiotic efficacy will have dire consequences for human morbidity and mortality, there is an urgent need for a comprehensive and global strategy to forestall the development of resistance to antibiotics by bacterial pathogens. Action must include steps to promote the judicious use of antibiotics in human medicine and in animal production, and to mitigate terrestrial and aquatic exposure to antibiotic residues and antibiotic resistance genes carried in agricultural wastes, and effluents from municipal wastewater treatment. It is important that in mixed agriculture, livestock and crop production systems be tightly coupled with respect to nutrient flow. Manures typically carry antibiotic-resistant bacteria, and numerous genes associated with antibiotic resistance determinants have been detected in molecular inventories of manure microbial populations, and in the environment in proximity to land fertilized with manure. In field experiments in London Ontario, we have been evaluating the dynamics of antibiotic resistance genes (ARGs) and bacteria following the land application of dairy or swine manure, or sewage sludge, and whether the use of these materials as soil amendments in normal farming practice increases the abundance of ARGs on crops at harvest. Following a general introduction to antibiotic resistance, this presentation will present recent search results, (eg. Applied and Environmental Microbiology 79:5701-9; 80:3258-65; 80:6898-6907) and discuss their potential significance within the broad context of antibiotic resistance development. Key findings are that soils become enriched with DNA carried in amendments including genes associated with antibiotic resistance and gene mobility. Antibiotic resistance genes persisted for months following soil amendment with seasonally variable and complex dynamics. Vegetable crops harvested in the fall following a spring amendment application carried an additional burden of ARGs, compared to crops grown in unamended soil. Further knowledge concerning the origin and dynamics of ARGs in animal and crop production systems is needed to inform agricultural policies and practices that mitigate human exposure to antibiotic resistant bacteria entrained on food crops.
Keywords: Antibiotic resistance, manure, soil.