Systematic review of wild birds as reservoirs of antimicrobial resistance: Implications for roof-harvested rainwater safety

This review investigates the role of wild birds as reservoirs and vectors of antimicrobial-resistant bacteria and antimicrobial resistance genes, and the implications for human health via contamination of harvested rainwater. A systematic literature review revealed that urban-adapted birds, especially gulls and pigeons, frequently carry clinically relevant antimicrobial-resistant bacteria including Carbapenem resistant Enterobacterales (CRE), multidrug-resistant Escherichia coli, extended-spectrum beta-lactamases (ESBL)-producing E. coli, and methicillin-resistant Staphylococcus aureus (MRSA) as well as colistin and macrolide-lincosamide-streptogramin (MLS) resistance genes. Due to urbanisation, these birds often forage in contaminated urban environments such as landfills, sewage sites and waste deposits, which increases their exposure to antimicrobial-resistant bacteria and antimicrobial resistance genes raising concerns about their increasing role in the environmental dissemination of AMR. Roof-harvested rainwater, a growing alternative water source amid climate change and water scarcity, can be contaminated by bird droppings containing antimicrobial-resistant bacteria and antimicrobial resistance genes. Despite its widespread use, harvested rainwater remains largely unregulated, presenting a public health risk. The findings from this review highlights the need for increased monitoring, targeted research, and improved risk management strategies to address AMR transmission from birds to humans via environmental pathways such as harvested rainwater.