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Antibiotic resistance genes and antibiotic resistant bacteria as emerging contaminants in wastewater: fate and persistence in engineered and natural environments(2018-12) [Dissertation]
Advisor: Hong, Pei-Ying
Committee members: Plewa, Michael J.; Daffonchio, Daniele; Saikaly, PascalThe emergence and rapid spread of antimicrobial resistance (AMR) is a phenomenon that extends beyond clinical settings. AMR has been detected in multiple environmental compartments, including agricultural soils and water bodies impacted by wastewater discharges. The purpose of this research project was to evaluate what factors could influence the environmental persistence of antibiotic resistance genes (ARGs), as well as to identify potential strategies employed by human pathogens to survive in secondary environment outside the host. The first part of this dissertation describes the incidence of the New Delhi metallobeta lactamase gene (blaNDM-1) – an ARG conferring resistance to last resort antibiotics – in the influent of a wastewater treatment facility processing municipal wastewater from Jeddah, Saudi Arabia. Detection of blaNDM-1 was followed by the isolation of a multi-drug resistant strain of E. coli (denoted as strain PI7) at a frequency of ca. 3 x 104 CFU/m3 in the untreated municipal wastewater. Subsequently, we described the decay kinetics of E. coli PI7 in microcosm experiments simulating biological treatment units of wastewater treatment plants. We identified that transition to dormancy is the main strategy prolonging the persistence of E. coli PI7 in the microcosm experiments. Additionally, we observed slower decay of E. coli PI7 and prolonged stability of extracellular DNA in anoxic/anaerobic conditions. In the last chapter of this thesis, the fate of extracellular DNA is further explored. Using as a model Acinetobacter baylyi ADP1, we describe the stimulation of natural transformation frequencies in the presence of chlorination disinfection byproducts (DBPs). Moreover, we demonstrate the ability of BAA to stimulate transformation is associated with its capacity to cause DNA damage via oxidative stress. Overall, this dissertation addresses important knowledge gaps in our current understanding of ARB and extracellular ARG persistence in the environment. The results from this project highlight the importance of retrofitting the existing water treatment process with advance membrane filtration units, and the need to relook into the current disinfection strategies. Wastewater treatment technologies should be assessed for their efficacies in not only inactivating ARB and ARGs, but also whether unintended consequences such as stimulated horizontal gene transfer would occur. -
Removal of antibiotic-resistant bacteria and antibiotic resistance genes affected by varying degrees of fouling on anaerobic microfiltration membranes(Environmental Science & Technology, American Chemical Society (ACS), 2017-10-10) [Article]An anaerobic membrane bioreactor was retrofitted with polyvinylidene fluoride (PVDF) microfiltration membrane units, each of which was fouled to a different extent. The membranes with different degrees of fouling were evaluated for their efficiencies in removing three antibiotic-resistant bacteria (ARB), namely, blaNDM-1-positive Escherichia coli PI-7, blaCTX-M-15-positive Klebsiella pneumoniae L7, and blaOXA-48-positive E. coli UPEC-RIY-4, as well as their associated plasmid-borne antibiotic resistance genes (ARGs). The results showed that the log removal values (LRVs) of ARGs correlated positively with the extent of membrane fouling and ranged from 1.9 to 3.9. New membranes with a minimal foulant layer could remove more than 5 log units of ARB. However, as the membranes progressed to subcritical fouling, the LRVs of ARB decreased at increasing operating transmembrane pressures (TMPs). The LRV recovered back to 5 when the membrane was critically fouled, and the achieved LRV remained stable at different operating TMPs. Furthermore, characterization of the surface attributed the removal of both the ARB and ARGs to adsorption, which was facilitated by an increasing hydrophobicity and a decreasing surface ζ potential as the membranes fouled. Our results indicate that both the TMP and the foulant layer synergistically affected ARB removal, but the foulant layer was the main factor that contributed to ARG removal.
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Reusing Treated Wastewater: Consideration of the Safety Aspects Associated with Antibiotic-Resistant Bacteria and Antibiotic Resistance Genes(Water, MDPI AG, 2018-02-27) [Article]As more countries engage in water reuse, either intended or de facto, there is an urgent need to more comprehensively evaluate resulting environmental and public health concerns. While antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) are increasingly coming under the spotlight, as emerging contaminants, existing water reuse regulations and guidelines do not adequately address these concerns. This perspectives paper seeks to frame the various challenges that need to be resolved to identify meaningful and realistic target types and levels of antibiotic resistance benchmarks for water reuse. First, there is the need for standardized and agreed-upon methodologies to identify and quantify ARB and ARGs. Second, even if methodologies are available, identifying which ARB and ARGs to monitor that would best relate to the occurrence of disease burden remains unknown. Third, a framework tailored to assessing the risks associated with ARB and ARGs during reuse is urgently needed. Fourth, similar to protecting drinking water sources, strategies to prevent dissemination of ARB and ARGs via wastewater treatment and reuse are required to ensure that appropriate barriers are emplaced. Finally, current wastewater treatment technologies could benefit from modification or retrofit to more effectively remove ARB and ARGs while also producing a high quality product for water and resource recovery. This perspectives paper highlights the need to consider ARB and ARGs when evaluating the overall safety aspects of water reuse and ways by which this may be accomplished.
