Date Full Report Received


Date Abstract Report Received



Primary Investigator:

The use of antibiotics by the swine industry to increase production efficiency and treat disease is thought to contribute to antibiotic resistance in the environment. When manure from hog operations is applied to fields with subsurface drainage, it is possible that the antibiotics and bacteria with resistance will be transported through tile systems and discharged into surface waters. To investigate this, tylosin, enterococci (a pathogen indicator organism), and antibiotic resistance genes (ARGs) were assessed in manure, soil and tile water samples. The ARG examined in this study were the erm genes which confer resistance to macolide anibiotics, including tylosin and erythromycin. Manure from a swine facility which administers tylosin at sub-therapeutic levels was applied to chisel plow and no-till plots with separate tile drains. The use of tylosin in swine production caused an increase in erm genes in manure and in manured-treated soil above the background levels of erm genes in soils not receiving manure. This increase in soil is greatest immediately after manure application; and ermB and ermF persist in manure injection band in concentrations greater than in non-manured soils over winter. However, the manure band concentrations eventually decreased to levels equivalent to the non-manured control soils. This is potentially due to a reduction in erm-hosting bacteria in the soil following manure application. The same trend was seen in the decline of total enterococci populations over time potentially due to die off and other environmental factors, but enterococci were less persistent than erm genes after manure application. Tylosin concentrations are very low in the soil and water, and do not likely impact the selective pressures on erm genes in either matrix. Erm gene concentrations in tile water were not different between tillage or manure treatments, suggesting that off-site transport of erm genes was not increased by the application of manure from antibiotic-treated swine.

For questions, contact:
Michelle Soupir
Assistant Professor, Agricultural and Biosystems Engineering
Iowa State University
3163 NSRIC
Ames, IA 50011-3310