Dirty habits: potential for spread of antibiotic-resistance by black-headed gulls from waste-water treatment plants.

Anthropogenic environments such as wastewater treatment plants (WWTPs) and landfills are sources of antimicrobial resistance (AMR). Black-headed gulls (Chroicocephalus ridibundus) frequently use WWTPs and may be vectors for AMR. We used GPS tracking data for 39 gulls for up to 8 months, combined with a shedding curve, to study sources and dispersal distances of AMR in Iberia. The gulls used 21 different WWTPs (684 visits) and three landfills (21 visits). Areas of high risk of AMR dissemination were an average of 25 km from the infection source, with a maximum of 500 km. Solar saltworks and natural waterbodies were particularly exposed to AMR dissemination, followed by agriculture, sports facilities, and tourist beaches. There was important variability between individual gulls in their habitat specialization, and which WWTPs they visited. Studying the spatial movements of gulls after visiting WWTPs and landfills helps pinpoint sensitive locations where pathogen transmission is most likely.