Effect of storm events on transport of antibiotic resistance genes in surface water and sediment: Field studies in Colorado and Virginia

Increasing antibiotic resistance among bacteria is a growing public health concern, with one likely source of spread of antibiotic resistance genes (ARG) between bacteria being surface water and sediments, where ARGs may enter via a variety of sources, such as agricultural runoff and treated municipal wastewater discharge. While transport of ARGs from these sources to sediment is a suspected dominant mechanism of ARG transport and accumulation in watersheds, movement of sediment may play a key role in ARG transport. In September 2013, a catastrophic 500-year storm flooded the Cache La Poudre River (Fort Collins, CO), moving massive amounts of sediment and transforming the river landscape. To assess the impact of this sediment movement on the river's ARG population, water and sediment samples were collected at river sites of varying impact from urban and agricultural point and non-point sources, both before and after the flood. In addition, a second watershed (Stroubles Creek, Blacksburg, VA) was studied to investigate changes in ARG concentrations throughout the course of more typical storm events, where samples were collected at 15 minute intervals throughout three different storm events. Quantitative polymerase chain reaction was used to measure five ARGs (sul1, sul2, tet(W), tet(O), and erm(F)) for all samples as well as total 16S rRNA genes.