Effect of Animal Manure in Development of Antibiotic Resistance in Agricultural Land

The long-term effect of the common practice of treatment of agricultural land with animal manure on the emergence of antibiotic-resistant organisms is not well understood. Over the years, animal feeding operations have progressively increased in size and have become increasingly concentrated in certain geographical areas like the Midwest. Consequently, extremely large quantities of animal manure are dispersed as fertilizer in surrounding farmland. This manure contains large-quantities of enteric microorganisms that have been exposed to sub-therapeutic levels of antibiotics that are commonly used in animal agriculture and the manure also contain some unabsorbed antibiotics as well. Long-term treatment of soil with animal manure can not only introduce antibiotic-resistant bacteria to the soil, but also can convert native soil organisms to antibiotic resistant forms.

We have utilized a soil ecosystem that had been continuously treated with swine effluent, cattle manure, and anhydrous ammonia for 15 years as well as an adjacent plot of land that was maintained as an untreated control.  Prevalence and fluctuation of antibiotic resistant genes in the various soil samples were tested using a battery of PCR assays designed to detect the resistant genes.

The prevalence, intensity and diversity of antibiotic resistant genes over the 15-year time period will be discussed.