Antibiotic resistance is one of the biggest threats to human health. Due to the misuse of Βeta lactam (β-lactam) antibiotics, some Gram-negative Enterobacteriaceae have developed the genes to produce Extended Spectrum Beta Lactamase enzymes (ESBLs), which can render the antibiotic ineffective. In the last ten years, ESBL-producing Enterobacteriaceae such as blaCTX-M groups, blaTEM, blaSHV and blaOXA have risen very rapidly in many countries. Societal changes (e.g. greater international travel) increase the likelihood of ESBLs transmission as individuals excrete the resistant bacterial strains, which can then enter the wider environment through wastewater treatment plants (WWTPs). When WWTP discharge ESBL-producing Enterobacteriaceae into the water environment, bacteria can associate with suspended sediment particles, in particular during storm events, then transport a wide range area such as estuaries, the coastline, offshore, leading to be a risk for human health, food and wildlife. This PhD studentship aimed to improve our understanding of the fate of ESBL-producing Enterobacteriaceae within a WWTP and following subsequent release. Chapter 3 assessed the presence of ESBL-producing Enterobacteriaceae within the WWTP (influent, primary sediment tank, aeration tank and effluent) in the city of Bangor. The treatment of wastewater significantly reduced 99% (P-value <0.05) of presumptive E. coli and other faecal coliforms (OFCs) between the influent and effluent. However, ESBL-producing E. coli and OFCs were detected in effluent site (post UV-disinfection) 2/26 and 5/28, respectively. We estimate that 300 billion each of both ESBL-producing E. coli and OFCs enter the water environment per day through the effluent released from this WWTP. Overall, across all sampling times and points, ESBL genes were found in 4/123 of E. coli and 18/136 of OFCs. The blaCTX-M group 1 was the most frequent ESBL gene among E. coli, while blaSHV was most predominant in OFCs. In Chapter 4, we investigated how large changes to human population (before and after the students’ arrival during “welcome week”) might affect the presence of ESBL-producing Enterobacteriaceae in the WWTP. Of the E. coli isolated, a number of E. coli were ESBL-producers (7/208) before welcome week, and a similar number were found after students had arrived (6/238). However, there was an increase in the number of ESBL-producing OFCs recovered (18/155 before and 26/220 thereafter). Of note, the diversity of genes detected increased after the arrival of students (4 vs 6 for E. coli and 8 vs. 10 for OFC). The new bla genes detected after the arrival of students were blaCTX-M-14, (blaCTX-M-15 + blaOXA-1) and (blaCTX-M-27 + blaOXA-1) in E. coli. In OFCs, these were (blaTEM-1 + blaSHV-2), (blaTEM-19 + blaSHV-12 + blaOXA-1), (blaTEM-120 + blaSHV-12 + blaOXA-1) and blaSHV-12. blaCTX-M-15 was the most frequent enzyme-producing E. coli in both periods, while the most frequently detected ESBL gene among OFCs was blaSHV-2 and then blaTEM-19 before welcome week, but blaSHV-12 and then blaTEM-1 predominated thereafter. Chapter 5 simulated, in microcosms, the impact of suspended sediment concentrations (low, medium and high) on the inactivation rate of blaCTX-M-15-producing E. coli derived from human wastewater in seawater and freshwater under simulated duration of UV light in winter and summer of north Wales. Survival was greater under higher sediment concentrations, and was much better in freshwater than seawater. From all the experiments conducted, it shows that ESBL-producing Enterbacteriaceae is prevalent and persistent in WWTP, with an increase diversity of genes during population changes, and higher suspended sediment concentrations could be contribute to the survival of ESBL-producing Enterobacteriaceae in the water environment after discharging by WWTP. The presence of ESBL-producing Enterobacteriaceae in the water environment poses a risk for human health.