Theses and Dissertations from UMD
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Item WATER REUSE FOR FOOD PRODUCTION IN THE WEST BANK AND ISRAEL: ASSESSING THE EFFICACY OF HOUSEHOLD GREYWATER TREATMENT SYSTEMS, AND CONSUMER PERCEPTIONS OF REUSE APPLICATIONS(2019) Craddock, Hillary Anne; Sapkota, Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Greywater is increasingly reused for agricultural irrigation in the Middle East. However, there is a dearth of data regarding antibiotics, herbicides, and antibiotic-resistant bacteria in household greywater reuse systems. Additionally, there are minimal data assessing consumer perceptions of water reuse practices. To address these gaps, my dissertation aims were to: 1) evaluate the presence of antibiotics and herbicides in greywater and treated effluent; 2) assess the prevalence of antibiotic-resistant Enterobacteriaceae in greywater and treated effluent; and 3) explore consumer perceptions of water reuse practices in Israel and the West Bank. For Aims 1 and 2, household greywater (n=23), treated effluent (n=23) and pond water (n=12) were collected from four farms in the West Bank from October 2017 to June 2018. The presence of antibiotics and herbicides was quantified using high performance liquid chromatography-tandem mass spectrometry, E. coli were enumerated via membrane filtration, and isolates were tested for antimicrobial susceptibility using microbroth dilution. For Aim 3, surveys (n=236) were administered in Eilat, Israel and Bethlehem, West Bank. Statistical analysis included ANOVA, chi-squared, and Fisher’s exact tests. Multiple antibiotics and herbicides were detected in greywater influent. Removal during treatment was variable across compounds. The majority of influent (76.5%) and effluent (70.6%) samples had detectable levels of E. coli. Resistance was most commonly observed against ampicillin, trimethoprim-sulfamethoxazole, tetracycline, and cefazolin. Regarding consumer perceptions, >50% of Israeli respondents were willing to serve raw and cooked produce irrigated with reused water. Palestinian respondents were more willing to engage in high-contact uses than Israeli respondents. The successful completion of this research has advanced knowledge regarding 1) the persistence of chemical and microbiological contaminants in treated household greywater that is used for food crop irrigation; and 2) consumer acceptance of water reuse practices. Farmers in the West Bank and around the world are combating decreasing quality and quantity of water and will increasingly rely on consumers willing to purchase produce irrigated with treated wastewater. Future work must ensure that farmers have access to safe and abundant irrigation water, and that consumers can be confident that they are purchasing safe food.Item Small molecule inhibitors of cyclic di-AMP signaling(2018) OPOKU-TEMENG, CLEMENT; SINTIM, HERMAN O; JULIN, DOUGLAS; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Globally, it is estimated that more than 700,000 people die annually from infections caused by drug-resistant bacterial pathogens. Resistant strains of bacteria continue to be isolated in healthcare and community settings. At the same time, the antibiotic pipeline remains dry – exemplified by the paucity of new antibiotics introduced into clinical use. Consequently, antibiotic-resistant strains are rapidly spreading, and antibiotic-resistant infections persist. Additionally, the existing antibiotics target one of the common targets – DNA, RNA, protein and cell wall synthesis. There is an apparent need to identify antibacterial agents against novel targets to slow down the generation of resistance. Cyclic dinucleotides have emerged as central regulators of bacterial physiology. Particularly, cyclic di-AMP (c-di-AMP) regulates cell wall homeostasis, cell size, potassium ion transport, virulence and biofilm formation in various Gram-positive pathogens including Staphylococcus aureus, Enterococcus faecalis, Listeria monocytogenes and Streptococcus pneumoniae. It has been demonstrated that under standard laboratory conditions, deletion of the diadenylate cyclase genes that encode c-di-AMP synthesizing enzymes (diadenylate cyclase, DAC) was lethal in human pathogens like S. aureus and L. monocytogenes. Hence, DACs have been suggested as potential antibiotic targets. Thus far, the effect of c-di-AMP on bacterial physiology has been studied using genetic approaches whereby the key players of the second messenger signaling are deleted, inactivated or overexpressed to create conditions of varying intracellular c-di-AMP levels. However, these approaches are not amenable to drug development. Cell permeable small molecule modulator or c-di-AMP levels are required to validate the druggability of c-di-AMP signaling. This dissertation reports the identification of different small molecules that potently inhibit c-di-AMP synthesis. The cell permeable inhibitors possess the ability to decrease the intracellular concentration of c-di-AMP. Furthermore, the antibacterial activities of the cell permeable c-di-AMP synthesis inhibitors have been characterized. Efforts towards the development of antibiotics have also been discussed.