Date Full Report Received


Date Abstract Report Received



Primary Investigator:
Co-Investigators: Thomas Moorman, Matthew Helmers, Elizabeth Luby

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, ermC, 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 and dry soil conditions in summer and fall of 2012. 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 during the dry to average years of precipitation (2011 and 2012), but in 2013 when above average precipitation occurred significantly higher concentrations of ermB and ermF genes were observed in tile drainage from the manure amended plots. However, concentrations of erm genes observed in 2013 are similar to levels observed in our previous year of study.
For questions, contact:
Michelle Soupir
Iowa State University
Ames, IA 50011