Frequent contact with human waste and liquid manure from intensive livestock
breeding, and the increased loads of antibiotic-resistant bacteria that
result, are believed to be responsible for the high carriage rates of ESBL-
producing E. coli found in birds of prey (raptors) in Central Europe. To test
this hypothesis against the influence of avian migration, we initiated a
comparative analysis of faecal samples from wild birds found in Saxony-Anhalt
in Germany and the Gobi-Desert in Mongolia, regions of dissimilar human and
livestock population characteristics and agricultural practices. We sampled a
total of 281 wild birds, mostly raptors with primarily north-to-south
migration routes. We determined antimicrobial resistance, focusing on ESBL
production, and unravelled the phylogenetic and clonal relatedness of
identified ESBL-producing E. coli isolates using multi-locus sequence typing
(MLST) and macrorestriction analyses. Surprisingly, the overall carriage rates
(approximately 5%) and the proportion of ESBL-producers among E. coli
(Germany: 13.8%, Mongolia: 10.8%) were similar in both regions. Whereas
blaCTX-M-1 predominated among German isolates (100%), blaCTX-M-9 was the most
prevalent in Mongolian isolates (75%). We identified sequence types (STs) that
are well known in human and veterinary clinical ESBL-producing E. coli (ST12,
ST117, ST167, ST648) and observed clonal relatedness between a Mongolian avian
ESBL-E. coli (ST167) and a clinical isolate of the same ST that originated in
a hospitalised patient in Europe. Our data suggest the influence of avian
migratory species in the transmission of ESBL-producing E. coli and challenge
the prevailing assumption that reducing human influence alone invariably leads
to lower rates of antimicrobial resistance
