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

Abstract

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.

Keywords: Antibiotic resistance; Escherichia Coli; antibiotics; birds; gulls; wildlife.

Fig. 1

Geographical variation in gull E. coli resistance levels in nine different European countries. Dots represent sampling sites in each country, and the bar plots show average resistance levels (%) to each of the analysed antibiotics. The antibiotics, from left to the right: nalidixic acid (NA), streptomycin (S), tetracycline (TE), ampicillin (AMP), chloramphenicol (C), cefadroxil (CFR), tigecycline (TGC), nitrofurantoin (N), mecillinam (MEL) and trimethoprim/sulfamethoxazole (SXT). The bar plot from Spain is enlarged to indicate the scale used.

Fig. 2

Differences in antibiotic resistance levels between two sampling sites in Latvia. Bars shows the percentage of isolated E. coli with resistance to each tested antibiotic.