Carriage of ESBL-Producing E. coli in European Herring Gulls (Larus argentatus)

Abstract

Wild birds are normally not exposed to antimicrobial agents but can acquire antimicrobial resistant bacteria through contact with domesticated animals and environment. Residues of antibiotics disposed inappropriately can affect soil microbiota particularly in urban dumps where gulls are predominant fauna in recent years. The aim of this study was to determine the carriage of extended spectrum beta-lactamases (ESBL) producing Escherichia coli in the population of European herring gulls (Larus argentatus) and to characterize the isolates regarding antimicrobial resistance. Material/methods: One hundred samples of European herring gull faeces were collected on Kaunas city dump as well as on the pier of Ventes Ragas using sterile cotton swabs with transport medium (Transwab® Amies, UK). Material was inoculated onto Brilliance ESBL Agar (Thermo Scientific, UK) for screening of E. coli. Pink and blue colonies were selected and identified using GN-ID A biochemical identification system (Microgen, UK). ESBL-production was confirmed with the cefpodoxime/cefpodoxime + clavulanic acid double-disc test (Thermo Fisher, UK). Samples were regarded as ESBL producing and further analysed when zone diameter around cefpodoxime was ≥5 mm than the zone diameter around cefpodoxime + clavulanic acid, according to manufacturer’s instructions. Susceptibility testing was performed using Sensititre® ARIS incubating and reading system with “Sensititre” plates (Thermo Scientific, UK). Interpretation of results was based on EUCAST clinical breakpoints. Results: Seventeen samples of out of one hundred tested were positive for ESBL-producing E. coli (17.0%; CI 95 % 9.6-24.4). All of the isolates demonstrated resistance to monobactams. MIC of cefpodoxime toward 13 isolates was >8 mg/L and 2-4 mg/L toward 4 isolates. One isolate was resistant to imipenem. Thirteen isolates (76.5%) were resistant to ciprofloxacin. ESBL-producing isolates al