Antibiotic resistance patterns in Escherichia coli from gulls in nine European countries

Background: The prevalence of antibiotic resistant faecal indicator bacteria from humans and food production
animals has increased over the last decades. In Europe, resistance levels in Escherichia coli from these sources
show a south-to-north gradient, with more widespread resistance in the Mediterranean region compared
to northern Europe. Recent studies show that resistance levels can be high also in wildlife, but it is unknown to
what extent resistance levels in nature conform to the patterns observed in human-associated bacteria.
Methods: To test this, we collected 3,158 faecal samples from breeding gulls (Larus sp.) from nine European
countries and tested 2,210 randomly isolated E. coli for resistance against 10 antibiotics commonly used in
human and veterinary medicine.
Results: Overall, 31.5% of the gull E. coli isolates were resistant to ]1 antibiotic, but with considerable
variation between countries: highest levels of isolates resistant to ]1 antibiotic were observed in Spain
(61.2%) and lowest levels in Denmark (8.3%). For each tested antibiotic, the Iberian countries were either the
countries with the highest levels or in the upper range in between-country comparisons, while northern
countries generally had a lower proportion of resistant E. coli isolates, thereby resembling the gradient of
resistance seen in human and food animal sources.
Conclusion: We propose that gulls may serve as a sentinel of environmental levels of antibiotic resistant
E. coli to complement studies of human-associated microbiota.