Mitigation and Risk Assessment of Antimicrobial Resistance in Recycled Irrigation Water

The goal of this project is to assess the contribution of recycled water to antimicrobial resistance and to mitigate soil and crop contamination via bioaugmentation of degradation with plant growth-promoting rhizobacteria. We will identify the extent of the development of antimicrobial resistance in the field and examine the potential mitigation of food contamination in laboratory and greenhouse studies.Objective 1: Assess the contribution of agricultural irrigation water to the risk of antimicrobial exposure in bulb and leafy crops and to the development of antimicrobial resistance. Three farms in the South Texas Rio Grande Valley will be sampled. To understand the dynamics of the input and persistence of antimicrobials and ARGs, water, soil (bulk & rhizosphere), and plant tissues (onion and spinach) will be collected at three sampling times (early, midpoint, and late crop cycle). During the second year of the study, farms will be revisited to collect samples at two time points (early and late crop cycle) to compare results from the first year of the study.Objective 2: Determine the mitigation extent of antimicrobial accumulation in crops and soils by reducing contaminants using plant growth-promoting rhizobacteria. We have characterized 32 triclosan-degrading rhizobacteria with PGPR activities from onions that will serve as bioinoculants. Additional spinach rhizobacteria and PGPRs from field crops will be characterized. PGPRs will be tested for the biodegradation potential of targeted antimicrobials (benzalkonium chloride, tetracycline, and ciprofloxacin), other than our previous triclosan assays, by determining if the PGPRs use antimicrobials as a sole carbon source. Following the biodegradation screening study, isolates will be further screened for in situ effects on antimicrobial levels and ARG abundance in unplanted soils prior to finalizing the PGPR mixture inoculum for the irrigation study. A greenhouse irrigation study using onions and spinach will determine the effective reduction of antimicrobials by PGPR mixes and the mitigation capacity to reduce the selective pressure for antimicrobial resistance.