Treated wastewater contains antibiotic resistant bacteria and genes, and thus may be a point source that disseminates these elements to irrigated crops and soil, potentially contributing to the global scope of antibiotic resistance. Nonetheless, there is conflicting evidence regarding the persistence of antibiotic resistance constituents in natural environments, and therefore their epidemiological potential is unclear. The overall aim of this presentation is to explore the fate of antimicrobial resistance determinants in treated wastewater and irrigated soil and crops, and evaluate the capacity of wastewater-derived determinants to persist or proliferate following prolonged residence in the environment. We applied a holistic approach that combines several cutting edge methodologies including cultivation-based evaluation of multidrug resistant E. coli, qPCR/ddPCR quantification of antibiotic resistance genes, amplicon sequencing and shotgun metagenomics.
Collectively our data strongly indicates that antibiotic resistant bacteria and associated resistance genes persist poorly in irrigated crops and soil, and we determined that this is at least partially associated with the resilience of environmental microbiomes. Nonetheless, short-term inoculation of soil and produce in nutrient-rich medium resulted in regrowth of wastewater-derived multidrug resistant E. coli two weeks after going below detection levels, underlining the fact that “not detected” is not necessarily “not present”. Similar inoculation of treated wastewater- and freshwater-irrigated soils also promoted differences in microbiomes and resistomes that were not apparent in direct analyses of the soils, and these differences became more dramatic as a function of anthropogenic exposure. Collectively, our results demonstrate the power of ecosystem functioning in mitigating antimicrobial resistance; however, provide evidence that hazardous antibiotic resistance determinants may persist “under the radar”.
