Microdilution testing reveals considerable and diverse antimicrobial resistance of Escherichia coli, thermophilic Campylobacter spp. and Salmonella spp. isolated from wild birds present in urban areas

The antimicrobial resistance (AMR) of E. coli, Salmonella spp. and thermophilic Campylobacter spp. isolated from wild birds in the Austrian-Czech border region, predominantly within the vicinity of Vienna and Brno, was determined. Bacteria were isolated from cloacal swabs taken from 53 avian species belonging to 14 orders, the majority being feral pigeons and various songbirds. Consequently, 1978 E. coli, 24 Salmonella and 99 Campylobacter isolates were tested by microdilution method against a panel of 14 (E. coli and Salmonella spp.) or ten antimicrobial substances (Campylobacter spp.). The AMR varied greatly between Austrian and Czech isolates, between different bird and bacterial species and between the different antimicrobials without consistent trends being recognizable. In 331 from 664 birds, differences in the AMR profile between the two or three E. coli isolates from the same bird were observed. Concerning E. coli, the least effective antimicrobial was cephalotin (90.8% of isolates resistant); for Campylobacter it was trimethoprim-sulfamethoxazole (71.4% of isolates resistant). None of the antimicrobials was effective against all E. coli or Campylobacter isolates. In contrast, more than half of the antimicrobials were effective against all Salmonella isolates, but 71.4% of the Czech Salmonella isolates and all of the Austrian Salmonella isolates were multi-resistant (resistant to three or more antimicrobial substances); streptomycin being the least effective antimicrobial substance (90.5% of isolates resistant). It is concluded that AMR in zoonotic bacteria from wild birds in the investigated densely populated areas is widespread and diverse, arguing for certain care at the wildlife-human interface, but AMR to clinically important and critical antimicrobials is relatively low.