Page Banner

United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Understanding the Role of Commensal Anaerobic Bacteria in Odor, Emissions, and Antibiotic Resistance from Stored Livestock Manure

Location: Bioenergy Research Unit

2013 Annual Report


1a.Objectives (from AD-416):
Objective 1: Develop methods to reduce metabolic activity of microorganisms present in stored swine manure to decrease odor and gaseous emissions during storage. Objective 2: Characterize bacterial antibiotic resistance in swine feces and stored manure and potential for movement of resistance genes between bacterial species. Objective 3: Determine impact of natural plant compounds and/or their gut derived metabolites (e.g., tannins, pheophorbide, diterpenes) on levels of antibiotic resistance in commensal bacteria present in stored swine manure.


1b.Approach (from AD-416):
Intensification of modern livestock operations has resulted in the concentration of greater numbers of animals into fewer and fewer operations. This trend has also led to the inevitable concentration of manure generated by these facilities into increasingly smaller locations. In the Midwest, deep pit storage is the predominant method used to handle swine manure and this manure is a valuable renewable resource for use as fertilizer. However, concentration of manure has been accompanied by increased public concern about environmental impacts and public health. These include real and perceived fears of the effects of odors, volatile greenhouse emissions, and potential spread of antibiotic resistant microorganisms and genes. Therefore, research is needed to target the common factor relating these various concerns. This factor is the bacteria populations naturally found in manure and its precursor, animal feces. These bacteria are generally termed the commensal bacteria found in these two ecosystems (feces and manure). As a continuation of previous research in our laboratories, both classic microbiological methods as well as modern molecular biological approaches (i.e., direct 16S rDNA sequencing, quantitative real-time polymerase chain reaction (qRT-PCR)) will allow us to investigate the bacterial basis for production of odorous compounds, greenhouse gases such as methane, and the impact of using antibiotics in feed as growth promotants on antibiotic resistance present in the commensal bacterial populations. Research will be directed towards developing methods to reduce production of odors and emissions, identifying levels of antibiotic resistance in pure cultures, and identifying and quantitating resistance genes present in the manure. The potential for movement of such resistance genes between commensal bacteria and potential pathogens will also be investigated.


3.Progress Report:
In 2013, research continued on studying the inhibitory effects of quebracho and other tannins on production of total gas, methane, and the odorous compound hydrogen sulfide from manure slurry under laboratory conditions. Collaborative research was continued with a university partner on the combined effects of quebracho tannins and borax on inhibiting emissions from swine manure. This research applied biochemical techniques to quantify the effects of tannins and borax on the production of hydrogen sulfide and greenhouse gases. The optimal combinations of borax and tannins for emissions reduction were identified, and the effects of soils amended with treated manure on various crops (e.g., corn, soybean) were determined. This work relates to Objective 1 of the research project. Research also progressed on the analysis of microbial resistance to antibiotics in stored manure. The research resulted in the characterization of new organisms among those previously identified as antibiotic resistant. Polymerase chain reaction (PCR) assays were developed and used to survey swine feces and manure for the presence of selected antibiotic resistance genes. Using this approach, a number of genes for resistance to erythromycin and tetracycline were identified. Initial work was carried out on the effects of chlorophyll derivatives on reducing antibiotic resistance by pure bacterial cultures. This work relates to Objectives 2 and 3 of the research project. These results were communicated to the scientific community via presentations at domestic/international meetings and scientific publications.


4.Accomplishments
1. Chlorophyll derivatives alter the resistance of pure bacterial cultures to antibiotics. Bacteria commonly present in swine feces and stored manure may serve as reservoirs of antibiotic resistance genes and these genes may be transferred to pathogens present in these environments. Providing derivatives of the plant pigment chlorophyll to the gut of swine and stored manure may be a natural method for reducing particular types of antibiotic resistance. Agricultural Research Service, Bioenergy Research Unit scientists at the National Center for Agricultural Utilization Research, Peoria, Illinois, demonstrated that two metabolites of chlorophyll reduced the resistance of certain bacteria to antibiotics in pure culture. These results will aid in future research on methods to naturally reduce bacterial antibiotic resistance in the swine gastrointestinal tract and stored swine manure. Such reductions will be of benefit to swine producers, environmental protection agencies, health officials, and local residents that live near swine facilities.


Review Publications
Whitehead, T.R., Cotta, M.A. 2013. Stored swine manure and swine faeces as reservoirs of antibiotic resistance genes. Letters in Applied Microbiology. 56:264-267.

Cotta, M.A., Whitehead, T.R., Falsen, E., Moore, E., Lawson, P.A. 2013. Erratum to: Two novel species Enterococcus lemanii sp. nov. and Enterococcus eurekensis sp. nov., isolated from a swine manure storage pit. Antonie van Leeuwenhoek. 103:1409-1418.

Last Modified: 9/10/2014
Footer Content Back to Top of Page