Enrichment of antibiotic resistance genes in soil receiving composts derived from swine manure, yard wastes, or food wastes, and evidence for multi-year persistence of swine Clostridium spp.

The impact of amendment with swine manure composts (SMC), yard waste compost (YWC), or food waste compost (FWC) on the abundance of antibiotic resistance genes in soil was evaluated. Following a commercial-scale application of the composts in a field experiment, soils were sampled periodically for a decade, and archived air-dried. Soil DNA was extracted and gene targets quantified by qPCR. Compared to untreated control soil, all three amendment types increased the abundance of gene targets for up to four years post-application. The abundance of several gene targets was much higher in soil amended with SMC compared to soil receiving either YWC or FWC. The gene target ermB remained higher in the SMC treatment for a decade post-application. Clostridia were significantly more abundant in the SMC-amended soil throughout the decade following application. Eight percent of Clostridium spp. isolates from the SMC treatment carried ermB. Overall, addition of organic amendments to soils has the potentia...