P3-63 Metagenomic Analysis of Antibiotic Resistance Genes and Mobile Genetic Elements Found on Radish Taproots Grown in Soils Amended with Manure and Compost from Cattle

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Giselle Kristi Guron , Virginia Tech , Blacksburg , VA
Monica Ponder , Virginia Tech , Blacksburg , VA
Amy Pruden , Virginia Tech , Blacksburg , VA
Introduction:  Cattle are often treated with antibiotics, with their manure or composted manure used as a soil amendment for growing vegetables eaten raw. The effects of these agricultural practices on the produce microbial communities and antibiotic resistance genes (ARGs) are not well understood.

Purpose:  Metagenomics of microbial communities of vegetables can provide overviews of dominant ARGs present on vegetables. The objective of this study was sequence metagenomes of the microbial communities from greenhouse radish bulb surfaces that were grown in soils amended with manure or compost originating from dairy or beef cattle of different histories of antibiotic administration.

Methods: Beef cattle were administered chlortetracycline, sulfamethazine, and tylosin while dairy cattle were administered cephapirin and pirlimycin. Manure was collected from antibiotic-treated cattle and nontreated control cattle. The four manure types were composted using a static method. The four manure types and four compost types were amended to two soil types (sandy loam and silty clay loam), in addition to fertilizer controls. Radish seeds were directly sown, and DNA was collected from microbes dislodged off the surfaces of mature taproots. After Illumina HiSeq, metagenomic sequences were mined for ARGs using the Comprehensive Antibiotic Resistance Database.

Results:  Over 500 ARGs were identified among radish taproot surfaces. Some genes identified in all samples were dfrE, (trimethoprim resistance), rosB (polymyxin B resistance), and rosA (polymyxin B resistance). Genes that were not present on radishes grown in fertilizer control soils were ramA (multidrug resistance) and marA (induces transcription of efflux pump gene acrAB). However, those genes were present on radishes grown in soils amended with beef- and dairy-based manure and compost.

Significance: Further analysis will continue to identify ARGs. While ARGs will inevitably appear on vegetables regardless of biological soil amendment application, other ARGs can still be introduced into production by their use.