Ceftazidime avibactam

Antimicrobial susceptibility testing was performed on all isolates recovered from the two selective media using the disc diffusion method on Mueller–Hinton (MH) agar plates (Neogen, Lansing, Michigan) for ticarcillin (75 μg), amoxicillin/clavulanic acid (20–10 μg), cefotaxime (30 μg), ceftazidime (10 μg), temocillin (30 μg), cefoxitin (30 μg), ertapenem (10 μg), imipenem (10 μg), meropenem (10 μg), ceftazidime/avibactam (10–4 μg), aztreonam (30 μg), ciprofloxacin (5 μg), trimethoprim-sulfamethoxazole (SXT) (1.25–23.75 μg), tetracycline (30 μg), amikacin (30 μg), gentamicin (15 μg), and tobramycin (10 μg) (Bio-Rad Laboratories, Algés, Portugal), following EUCAST recommendations and breakpoint tables. Susceptibility to fosfomycin was evaluated by the disk diffusion method (50 μg) on MH agar plates supplemented with 25 μg/mL glucose-6-phosphate, according to EUCAST guidelines [24 ]. Strain E. coli ATCC 25922 was used for quality control. Multidrug resistance was defined as acquired non-susceptibility to at least one agent in three or more antimicrobial categories [25 (link)].

Antimicrobial susceptibility was tested by employing disk diffusion, gradient test, and broth microdilution test according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) recommendations, 2021 [43 ]. The disks impregnated with the following antimicrobial agents were tested: imipenem (10 μg), meropenem (10 µg), ciprofloxacin (5 µg), levofloxacin (5 µg), ceftazidime (10 µg), cefepime (30 µg), amikacin (30 µg), piperacillin/tazobactam (30/6 µg), aztreonam (30 µg), ticarcillin (75 µg), ceftazidime-avibactam (10–4 µg), and ceftolozane/tazobactam (38–10 µg) (BioRad, Watford, UK). Minimum inhibitory concentrations (MICs) for colistin, imipenem, and meropenem were evaluated by ComASP Colistin (Liofilchem, Roseto, Italy) and Gradient strip test (Liofilchem, Roseto, Italy), respectively. P. aeruginosa ATCC 27853 was used as the control strain in the antibiotic susceptibility testing. MDR P. aeruginosa were defined as isolates that tested resistant to at least one antimicrobial agent of three or more different classes. Extensively drug-resistant (XDR) P. aeruginosa were defined as a subset of MDR isolates that tested non-susceptible to at least one antimicrobial agent of five different classes. P. aeruginosa was defined as pandrug-resistant (PDR) when the organism was resistant to all tested agents.