Grants and Fellowships | 2014

24 Multi-Year Research Grants Effect of Treated Wastewater Irrigation on Antibiotic Resistance in Agricultural Soil Bacteria Antibiotic resistance (AR) is a global phenomenon with severe epidemiological ramifications. Anthropogenically-impacted natural environments can serve as reservoirs of antibiotic resistance genes (ARG), which can be horizontally transferred to human pathogens through water and food webs. Treated-wastewater (TWW) irrigation is widespread in arid regions of the world and especially in Israel (~50% of water used for agriculture), due to growing demand and diminishing freshwater supplies. However, wastewater effluents may contain residual concentrations of antibiotics, antibiotic- resistant bacteria (ARB), and ARGs, which can stimulate proliferation of AR in irrigated soil microcosms. To assess this hypothesis, we conducted comprehensive source tracking of ARB and ARGs in WWTP effluents and in freshwater- and TWW-irrigated soils; and determined the quantitative impact of residual levels of antibiotics on the abundance and diversity of ARB and ARGs in soil microcosms. High levels of antibiotic resistance were detected in all soils analyzed; however, contrary to our hypothesis, ARB and ARG levels were identical in the TWW- and freshwater- irrigated soils, despite the fact that high levels of resistant bacteria and genes were found in the TWW that was used for irrigation. Bench-scale soil microcosms irrigated with different levels of the antibiotic ciprofloxacin, showed negligible differences in the microbial community composition and the levels of resistant bacteria in the soils even when antibiotic concentrations were an order of magnitude higher than concentrations traditionally found in wastewater effluents. This strongly suggests that residual concentrations of antibiotics from wastewater do not result in proliferation of antibiotic resistance in the soil microbiome. Collectively our results show that the high levels of AR bacteria and ARGs in both the freshwater- and the TWW-irrigated soils are indicative of high levels of native AR in natural soil microbiomes. Although more comprehensive research is necessary, our results suggest that irrigation with recycled water does not significantly increase ARG reservoirs in soil, and therefore are cause for cautious optimism. Future research in our lab will specifically focus on assessing mobile genetic elements that carry ARGs in both wastewater effluents and in native soils. These mechanisms are of significant epidemiological potential because they can be horizontally transferred to clinically-relevant bacteria. Research publications (1) Negreanu, Y., Pasternak, Z., Jurkevitch, E., & Cytryn, E. (2012). Impact of treated wastewater irrigation on antibiotic resistance in agricultural soils. Environmental Science & Technology, 46 , 4800-4808. (2) Cytryn, E. (2013). The soil resistome: The anthropogenic, the native, and the unknown. Soil Biology & Biochemistry, 63 , 18–23. (3) Gatica, J., & Cytryn, E. (2013). Impact of treated wastewater irrigation on antibiotic resistance in the soil microbiome. Environmental Science Pollution Research, 20 (6), 3529-3538. Eddie Cytryn 1 1. Agriculture Research Organization (ARO), Volcani Center 2010-2012