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).