Lagoon, anaerobic digestion, and composting of animal manure treatments impact on tetracycline resistance genes

Authors: Agga, Getahun; COUCH, MELANIE - Western Kentucky University; Parekh, Rohan; MAHMOUDI, FARANAK - Western Kentucky University; APPALA, KERRTHI - Western Kentucky University; KASUMBA, JOHN - Western Kentucky University; Loughrin, John; CONTE, ERIC - Western Kentucky University

Submitted to: Antibiotics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/13/2022
Publication Date: 3/15/2022
Citation: Agga, G.E., Couch, M., Parekh, R.R., Mahmoudi, F., Appala, K., Kasumba, J., Loughrin, J.H., Conte, E.D. 2022. Lagoon, anaerobic digestion, and composting of animal manure treatments impact on tetracycline resistance genes. Antibiotics. 11(3). Article 391. https://doi.org/10.3390/antibiotics11030391.
DOI: https://doi.org/10.3390/antibiotics11030391

Interpretive Summary: Antibiotics such as tetracyclines are used in animal production for the purpose of controlling and treating infections caused by bacteria. However, administered antibiotics and antibiotic resistant bacteria that can infect people are excreted from the animal body through feces and urine. Once excreted in animal manure, they are considered environmental pollutants. They lead to further development and propagation of antibiotic resistant bacteria contaminating leafy greens when raw manure is used as organic fertilizer. They also contaminate drinking and irrigation waters as a run-off from animal production facilities. Farms use lagoons as waste storage. Some farms use anaerobic digestion technology that converts animal manure into a usable energy while reducing the volume of the animal waste. The impact of lagoons and anaerobic digestion as waste management practices on antibiotic resistance genes needs evaluations. We summarized their impact on tetracycline resistance genes. Tetracycline is the most widely used antibiotic in animal productions.

Technical Abstract: Increased demand for animal protein is met by increased food animal production resulting in large quantities of manure. Animal producers, therefore, need sustainable agricultural practices to protect environmental health. Large quantities of antimicrobials are used in commercial food animal production. Consequently, antimicrobial-resistant bacteria and the resistance genes emerge and are excreted through feces. Manure management is essential for the safe disposal of animal waste. Lagoons, with or without covers, and anaerobic digesters, with the primary purpose of methane production, and composting, with the primary purpose of producing organic fertilizer, are widely used methods of manure treatment. We reviewed manure management practices and their impact on tetracycline resistance genes. Lagoons are maintained at ambient temperatures; especially uncovered lagoons are the least effective in removing tetracycline resistance genes. However, some modifications can improve the performance of lagoons: sequential use of uncovered lagoons and the use of covered lagoons resulted in a one-log reduction, while post-treatments such as biofiltration following covered lagoon treatment resulted in 3.4 log reduction. Mesophilic digestion of animal manure did not have any significant effect; only a 0.7 log reduction in tet(A) was observed in one study. While thermophilic anaerobic digesters are effective, if properly operated, they are expensive for animal producers. Aerobic thermophilic composting is a promising technology if optimized with its economic benefits. Composting of raw animal manure can result in up to a 2.5 log reduction, and postdigestion composting can reduce tetracycline resistance gene concentration by >80%. In general, manure management was not designed to mitigate antimicrobial resistance; future research is needed to optimize the economic benefits of biogas or organic fertilizer on the one hand and for the mitigation of foodborne pathogens and antimicrobial resistance on the other.