Tazobactam

The isolates were initially processed using disk-diffusion antimicrobial susceptibility testing for amikacin, aztreonam, cefepime, ceftazidime, ciprofloxacin, doripenem, gentamicin, imipenem, levofloxacin, meropenem, netilmicin, piperacillin-tazobactam, ticarcillin-clavulanate, and tobramycin with Oxoid (Basingstoke, United Kingdom) disks. Complementarily, an in-house broth microdilution method using cation-adjusted Mueller–Hinton Broth (Sigma-Aldrich, St. Louis, MO, USA) was performed to determine the minimum inhibitory concentration (MIC) for amikacin gentamicin, imipenem, meropenem, colistin, polymyxin B, tigecycline, and ceftazidime-avibactam, and all salts were purchased from Sigma-Aldrich (St. Louis, MO, USA), except for avibactam, which was donated by Pfizer Inc. To complete the antimicrobial susceptibility panel, novel antimicrobials/combinations were evaluated with Liofilchem (Roseto degli Abruzzi, Italy) MIC test strips for ceftolozane–tazobactam, meropenem–vaborbactam, imipenem–relebactam, cefoperazone–sulbactam, cefiderocol, plazomicin, eravacycline, and fosfomycin.

The MIC of β-lactams and β-lactamase inhibitors (BLIs) was determined by the standard Clinical and Laboratory Standards Institute (CLSI) broth microdilution method (43 ). Imipenem was purchased from Fresenius Kabi (Barcelona, Spain); meropenem from Aurovitas (Madrid, Spain); ertapenem from Merck Sharp & Dohme (Haarlem, Netherlands); penicillin G from Laboratorio Reig Jofré SA (Barcelona, Spain); ceftaroline from Pfizer Pharmaceuticals (Ringsend, Ireland); cefotaxime, ceftriaxone, cefoxitin, and ceftazidime from Laboratorios Normon (Madrid, Spain); cefepime from Accord Healthcare (Barcelona, Spain); aztreonam from Bristol-Myers Squibb (Madrid, Spain); and doripenem, cefixime, ceftolozane, amdinocillin, carbenicillin, piperacillin, ticarcillin, avibactam, relebactam, sulbactam, and tazobactam from MedChem Express (Sollentuna, Sweden). ceftazidime-avibactam and ceftolozane-tazobactam MICs were determined by MIC test strip from Liofilchem (Rosetto degli Abruzzi, Italy). MIC values were determined from at least three independent experiments.