Phoenix m50 automated microbiology system

The minimal inhibitory concentrations (MICs) of all isolates were determined by broth microdilution method using the BD Phoenix^TM M50 Automated Microbiology System (BD, San Jose, CA, USA). Nineteen antimicrobial agents were tested in this study, including colistin (PB, 0.25–8 μg/mL), chloramphenicol (CHL, 4–32 μg/mL), tetracycline (TET, 1–16 μg/mL), ampicillin (AMP, 2–32 μg/mL), cefoxitin (FOX, 2–64 μg/mL), nalidixic acid (NA, 4–32 μg/mL), ciprofloxacin (CIP, 0.015–2 μg/mL), amikacin (AMK, 4–64 μg/mL), nitrofurantoin (F, 32–256 μg/mL), ampicillin-sulbactam (SAM, 1–32 μg/mL), ceftazidime-avibactam (CZA, 0.25/4–8/4 μg/mL), azithromycin (AZM, 2–64 μg/mL), aztreonam (ATM, 0.25–16 μg/mL), cefotaxime (CTX, 0.25–16 μg/mL), ceftazidime (CAZ, 0.25–16 μg/mL), imipenem (IPM, 0.25–8 μg/mL), meropenem (MEM, 0.125–8 μg/mL), ertapenem (ETP, 0.25–8 μg/mL), and trimethoprim-sulfamethoxazole (SXT, 0.5–8 μg/mL). The qualitative interpretations of susceptible (S), intermediate (I), or resistant (S) strains were determined according to the standard of the Clinical Laboratory Standards Institute guidelines (CLSI 2020). Multidrug resistance (MDR) was defined as resistance to at least one agent in three or more antimicrobial classes [38 (link)].

The BD Phoenix^TM M50 Automated Microbiology System (BD, San Jose, CA, USA) was used to determine the minimal inhibitory concentrations (MICs) of 19 antimicrobial agents according to the manufacturer’s instructions, as previously described [63 (link)]. The antimicrobial agents include ampicillin–sulbactam (SAM, 1–32 µg/mL),trimethoprim–sulfamethoxazole (SXT, 0.5–8 µg/mL), meropenem (MEM, 0.125–8 µg/mL), colistin (PB, 0.25–8 µg/mL), ceftazidime–avibactam (CZA, 0.25/4–8/4 µg/mL), nitrofurantoin (F, 32–256 µg/mL), tetracycline (TET, 1–16 µg/mL), ertapenem (ETP, 0.25–8 µg/mL), ceftazidime (CAZ, 0.25–16 µg/mL), chloramphenicol (CHL, 4–32 µg/mL), imipenem (IPM, 0.25–8 µg/mL), ampicillin (AMP, 2–32 µg/mL), cefoxitin (FOX, 2–64 µg/mL), cefotaxime (CTX, 0.25–16 µg/mL), nalidixic acid (NA, 4–32 µg/mL), azithromycin (AZM, 2–64 µg/mL), ciprofloxacin (CIP, 0.015–2 µg/mL), aztreonam (ATM, 0.25–16 µg/mL), and amikacin (AMK, 4–64 µg/mL). Multidrug resistance (MDR) was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories [64 (link)].