2.3. Isolation, bacterial identification, and antimicrobial susceptibility testing
Cloacal, celomic and oral cavity and tissue swab samples were streaked onto blood and MacConkey agar plates and incubated overnight at 35±2 °C. Bacterial isolates were identified by the MALDI-TOFMS system (Bruker Daltonik), and clonal relationships among Escherichia coliisolates were determined by enterobacterial repetitive intergenic consensus (ERIC)–PCR (Da Silveira et al., 2002).
Antimicrobial susceptibility testing was performed by the disk diffusion method using human and veterinary antimicrobials (CLSI, 2018, 2020), including amoxicillin/clavulanate, ceftriaxone, cefotaxime, ceftiofur, ceftazidime, cefepime, cefoxitin, aztreonam, imipenem, meropenem, ertapenem, nalidixic acid, enrofloxacin, gentamicin, amikacin, trimethoprim-sulfamethoxazole and tetracycline. E. coli ATCC 25922 was used as control strain. Extended-spectrum β-lactamase (ESBL) production was screened by the double-disk synergy test (DDST) (Jarlier, Nicolas, Fournier,& Philippon, 1988).