Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 11, 2009
Publication Date: November 1, 2009
Citation: Brooks, J.P., McLaughlin, M.R. 2009. Antibiotic Resistant Bacterial Profiles of Anaerobic Swine Lagoon Effluent. Journal of Environmental Quality. 38:2431-2437. Interpretive Summary: Land application of swine lagoon effluent is a common practice for disposal of this nutrient-rich fertilizer. Effluent is a by-product of the swine-production industry and can contain common bacteria and pathogenic human bacteria which can carry antibiotic-resistance. Animal agriculture uses antibiotics as either a disease preventative or therapeutic treatment. Land application practices meant to capture nutrients, especially N and P, coincidentally treat bacterial pathogens, but antibiotic-resistant bacteria are largely forgotten. This study determined the presence and resistance patterns of antibiotic-resistant bacteria in swine manure lagoons on sow, nursery and finisher farms. The study found that farm type influenced antibiotic resistance patterns and indicated that nurseries had the greatest amount of resistance. In nurseries weaned pigs, vulnerable to disease, often receive preventative or therapeutic antibiotics. Most of the resistance, however, was characterized as natural rather than acquired resistance, although acquired resistance to some antibiotic classes was found. Potential impacts of antibiotic-resistant bacteria in effluent applied to crop land, on natural soil bacteria and public health are unknown and should be addressed in future research. Findings from this study will be of interest to agricultural scientists, swine producers and regulatory agencies charged with protecting public health.
Technical Abstract: Although land application of swine manure lagoon effluent is a common and effective method of disposal, the presence of antibiotic-resistant bacteria, both pathogenic and commensal can complicate already understood issues associated with its safe disposal. The aim of this study was to assess antibiotic resistance in swine lagoon bacteria from sow, nursery, and finisher farms in the southeastern United States. Effluents from 37 lagoons were assayed for the presence of Escherichia coli, Campylobacter, Listeria, and Salmonella. Antibiotic resistance profiles were determined by the Kirby-Bauer swab method for 12 antibiotics comprising 8 classes. Statistical analyses indicated that farm type influenced the amount and type of resistance, with nurseries and sow farms ranking as most influential, probably due to use of more antibiotic treatments. Finisher farms tended to have the least amount of antibiotic class resistance, signaling an overall healthier market pig, and less therapeutic or prophylactic antibiotic use. Many bacterial isolates were resistant to penicillin, cephalosporin, and tetracycline class antibiotics, while nearly all were susceptible to quinolone antibiotics. This is consistent with work which identified tetracycline as a common constituent of antibiotic cocktails administered to swine. Although antibiotic resistance levels in the present study differed by swine farm type, much of the resistance appeared to be natural or intrinsic, rather than acquired, which is reassuring when considering recent public health concerns.