Sentinel or Disperser? The Role of White Storks (Ciconia ciconia) in the Spread of Antibiotic-Resistant Bacteria

Antimicrobial resistance (AMR) represents a threat to human, animal, and environmental health. This study evaluated the potential role of birds as AMR dispersers in white storks as a model species investigating dispersal between locations connected by their movements. Throughout a year, 346 samples were collected from two landfills (225 fecal samples) and two wetlands (93 fecal/28 water samples) based on satellite tracking data that confirmed continuous stork movements between foraging (landfill) and nighttime roosting (wetlands) locations. Samples were seeded in selective media with antibiotics for the isolation of antibiotic-resistant bacteria. A total of 313 isolates from 35 different bacterial species were obtained, with an AMR prevalence of 43.1% in fecal samples from landfills, 7.5% in fecal samples from wetlands, and 21.4% in water from wetlands. Multidrug resistant bacteria were only found in fecal samples (19.6% landfills/4.3% wetlands) and extended-spectrum beta-lactamase producing-bacteria were found exclusively in fecal samples from landfills with a marked presence during the fall migration period. Our study reveals marked differences in AMR prevalence and resistance phenotypes between study locations and fecal and water samples throughout the year, thus not supporting a clear role of storks as AMR dispersers. Nevertheless, similar changes in AMR phenotype prevalences during fall migration in stork faecal samples from one of the tested landfills and its paired wetland, and the significant increase in ESBL-producing Enterobacterales prevalence matching the arrival of migratory white storks in fall, underline the need for more in-depth genome-based studies to elucidate the role of white storks as dispersers or sentinels of AMR.