Risk ranking of antimicrobial sources and antibiotic resistant organism exposure assessment

Antibiotic resistance within pathogenic bacteria is a major threat to human health worldwide. Several international authorities, such as the World Health Organization and United Nations have described antibiotic resistant bacteria (ARB) as a crisis facing global health. The presence of antibiotic residues in surface waters, which enter the environment as a result of use in human healthcare and agricultural use, have the potential to select for antibiotic resistance in bacterial populations. Once present in the environment, ARB can cause human health complications through a variety of exposure pathways. Risk assessment methods are invaluable tools, used throughout the literature to quantify the risks of both antibiotic resistance development and risk of human exposure and infection. This thesis aimed to use risk assessment methodologies to examine the pathways and potential levels of antibiotics entering Irish surface water bodies, their potential to facilitate antibiotic resistance development, and the resultant risks to human health arising from that resistance in Irish surface waters. The results of this work present several key findings. Knowledge gaps regarding antibiotic release and ARB presence in Irish surface waters were identified. Appropriate risk assessment methods from the literature for examining resistance development and exposure potential were highlighted. The work quantified the higher potential for antibiotic resistance development arising in surface waters as a result of human antibiotic administration versus agricultural use. Macrolides, in particular clarithromycin, were identified as being of particular risk for resistance development, as well as azithromycin being of particular risk for impact on cyanobacteria, algae, and other non-target organisms in the environment. The risk of human illness arising from recreational water use at sewage-impacted sites was quantified, as well as methods of mitigating human health risk discussed. Finally, the importance of adherence to thorough cooking of shellfish tissues originating from sewage-impacted waters to reduce the risk of ARB infection was highlighted. Future work in this field should seek to establish both regular testing of Irish water bodies for both ARB and antibiotic residues, and quantification of specific dose-response models for ARB. This thesis demonstrates both the serious risk from ARB to human health, as well as the value of risk assessment methodologies in quantifying risk, and translating scientific knowledge into actionable research and policy.