Progress 10/01/06 to 09/30/07
Outputs
OUTPUTS: The presence of antimicrobial agents in the environment and food chain has become a matter of increasing concern to the scientific community and the public at large. Large amounts of antimicrobials are used in food animal production and can enter the agroecosystem in biologically active form when manures are land-spread to serve as nutrient source to growing crops. While contributing to maintenance of animal health, use of veterinary antimicrobials may have unforeseen consequences on ecosystem function. Given that little is currently known about effects of these antimicrobials in the environment, we conducted a research program with two main objectives; a comprehensive review of the literature, and a laboratory study in which three antimicrobials commonly used on food animals were added to a soil-manure mixtures and the response of native soil microorganisms examined. The literature review produced a database of approximately 150 recent publications, divided into review papers, antimicrobial kinetics, occurrence in the agroecosystem, development of resistance in pathogens, effects on microbial communities, issues in human and animal health, and other topics. A summary of the literature is included in our journal article, refer to the Publications section of this report. Selected parts of the database were disseminated to interested researchers at University of Maryland and Louisiana State University. Results and analysis from the laboratory incubation study have been shared with colleagues, and given as poster presentations at the University of Pennsylvania's School of Veterinary Medicine faculty research exposition in May, 2007, and at the Tri-Societies International Annual Meetings in New Orleans in November 2007. An oral presentation of findings was given at the Northeast Regional ASA Meetings in June 2007. Results have been submitted to a peer-reviewed journal. Findings have also been incorporated into University of Pennsylvania's food animal medicine coursework, including Animal Production Systems, Dairy Production Medicine, and Animal Health Economics. PARTICIPANTS: Individuals (University of Pennsylvania): Dr. Zhengxia Dou, Assoc. Prof. Animal Production Systems, environmental soil science and soil chemistry. Dr. Shelley Rankin, Asst. Prof. Microbiology, Director of Salmonella Reference Center, veterinary microbiology. Dr. Helen Aceto, Asst. Prof. Epidemiology, Biosecurity official for New Bolton Center large animal research facility, epidemiology. Collaborators: Dr. Yucheng Feng, Auburn University, Assoc. Prof. Soil Science, soil microbiology and biochemistry. Dr. Qiquan Wang, Delaware State University, Asst. Prof. Chemistry, soil chemistry. TARGET AUDIENCES: Target audiences include food animal producers, the research community interested in implications of food animal production on agroecosystem function, and the general public. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
There is at present a lack of detailed knowledge about possible effects of veterinary antimicrobials in the agroecosystem, of which a fundamental part is the soil, with its microorganismal component and metabolism. The comprehensive literature review allowed us to understand the current state of understanding concerning implications of antimicrobials on animal, and by extension, human health, and ecosystem function. Our laboratory study inoculated poultry manure with either sulfadimethoxine or chlortetracycline, both widely used in the poultry industry, which was then mixed with silt loam soil and incubated for 50 days. Similarly, dairy manure with the ionophore monensin was mixed with soil and incubated. Microbial rates were chosen based on literature information on concentrations found in soil. Soil-manure subsamples were taken periodically and analyzed for soil respiration, nitrification, iron reduction, and community-level physiological profiles (CLPP). Important and novel results were obtained from the 50 day study, which will add to the store of knowledge about potentially deleterious effects in the complex, divserse and synergistic soil system. Although presence of antimicrobial agents generally had little effect on microbial respiration and nitrification, we identified two significant effects on iron reduction. Sulfadimethoxine almost completely inhibited iron reduction at all rates applied, and over the 50 day incubation. Monensin at all application rates had a strong inhibitory effect on iron reduction on day 1, while the drop in iron reduction lessened over time and was not found after day 15. Previous reports had suggested that monensin degrades in the soil over the course of weeks, which was confirmed by the present research. Community-level physiological profiles, which measures general metabolis function of a large proportion of the soil microorganisms, did not show a significant antimicrobial effect. We reason from the laboratory incubation study that the lack of antimicrobial effect on respiration, nitrification and CLPP was a function of the diversity of species employing those physiological pathways. Any types of microbes susceptible to antimicrobial effects would rapidly be replaced by other non-susceptible species. Iron reduction, on the other hand is a property of relatively few soil bacteria, and may be halted if those species are affected by various antimicrobial agents. Soil metabolic pathways are closely linked biochemically, therefore the loss or inhibition of one will have effects on others, in ways that are poorly understood. Data generated by this research program may be used by other interested parties, allowing the scientific and public communities to get a better idea of the larger implications of antimicrobial use in food animal production. Given the lack of knowledge about microbial ecosystem functions and the potential for disruption by chemicals introduced through human activity, continued research into potential effects of the presence of antimicrobial agents and their degradation products is warranted.
Publications
- Toth, J.D., Dou, Z., Ferguson, J.D., Ramberg, C.F., Jr., Wang, C., Rankin, S., Wang, Q., and Feng, Y. 2007. Effect of manure-borne veterinary antimicrobials on soil bacteria metabolic function. NEBSCA and American Forage and Grassland Council Joint Meetings, State College, PA, 26-26 June 2007. p. 1. (abstract).
- Toth, J.D., Dou, Z., Ferguson, J.D., Ramberg, C.F., Jr., Wang, C., Rankin, S., Wang, Q., and Feng, Y. 2007. Effect of veterinary pharmaceuticals on metabolic functions of native soil bacteria. ASA-CSSA-SSSA 2007 International Annual Meetings, New Orleans, LA, 4-8 November 2007. available online at http://a-c-s.confex.com/crops/2007am/techprogram/P36594.HTM. (abstract).
- Toth, J.D., Feng, Y., Ferguson, J.D., Ramberg, C.F., Jr., Wang, Q., and Dou, Z. 2009. Effect of veterinary antimicrobials on metabolism of soil microorganisms. Chemosphere (in review). (journal article).
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