Frequency and characterization of β-lactam-resistant Escherichia coli from wild birds from Marmara Region in Turkey

Abstract This study aimed to phenotypically and genotypically detect beta-lactam-resistant Escherichia coli in the feces of wild and migratory birds residing in or passing through the Marmara Region during seasonal migration. A total of 272 fresh fecal samples were non-invasively collected and grouped as follows: (1) resident wild waterfowl, (2) resident urban birds (e.g., pigeons, crows, sparrows), (3) migratory birds overwintering in Turkey, and (4) migratory birds staying during spring and summer. Samples were cultured on MacConkey agar with and without cefotaxime (1 mg/L). Carbapenem resistance was assessed using the Modified Hodge Test; none of the 212 isolates tested positive. Among the 272 birds sampled, 62 (22.8%) carried ESBL and/or AmpC producing isolates. Antimicrobial-resistant E. coli were identified in 59 of 272 birds (21.7%), including 47 ESBL-positive, 6 AmpC-positive, and 5 harboring both resistance types. Group 1 (mainly gulls) showed the highest resistance rates. PCR analysis revealed that among 84 isolates, 48 carried only beta-lactamase genes, 3 only AmpC genes, and 5 both. Detected genes included: bla CTX-M ( n = 50), bla SHV ( n = 2), and bla OXA10 ( n = 10); for AmpC: bla MOX ( n = 6) and bla CIT ( n = 2). Species-specific results confirmed the highest frequency of resistance genes in gulls. The Frequency of resistant isolates was significantly higher in Groups 1 and 2 ( P < 0.001). The resistance profiles identified in gulls especially those feeding at landfills or in direct contact with human, animal, and agricultural waste suggest a likely anthropogenic and/or zoonotic origin of the beta lactam resistance observed in this study conducted in Marmara Region.