2.1 Bacterial isolates
Enterobacteriaceae isolates were isolated from fresh fecal samples of animals at Zhengzhou Zoo, Henan province, China. Briefly, fecal samples were collocated into Eppendorf tube with 500μL sterile saline and shake gently and stood for 10 min. The supernatant was used to inoculate onto the MacConkey Agar (Beijing SanYao Science & Technology Development Co, Beijing, China) plate at 35oC for 18 hours. All the colonies with different morphologies and colors were stored and subjected to further analysis. Species identification was carried out using 16S rRNA sequence (TIANYI HUIYUAN,China).
2.2 DrugSusceptibility Testing
Drug susceptibility testing was performed by broth microdilution method (microbial susceptibility kit, BIO-KONT, China) according to the CLSI guidelines (CLSI,2019). Fifteen antimicrobial drugs were used to screen MDR in this study, including Ampicillin, Ampicillin/Sulbactam, Piperacillin/Tazobactam, Aztreonam, Cefuroxime sodium, Ceftriaxone, Cefepime, Ciprofloxacin, Levofloxacin, Meropenem, Colistin, Chloramphenicol , Trimethoprim/ Sulfamethoxazole, Nitrofurantoinand Amikacin . The Drug susceptibility to Tetracycline andDoxycycline was tested by Kirby-Bauer disk diffusion method (OXOID, UK), and E.coli ATCC25922 was used as a quality-control strain.