Susceptibility to cephalosporin combinations and aztreonam/avibactam among third-generation cephalosporin-resistant Enterobacteriaceae recovered on hospital admission

As part of the multicentre Antibiotic Therapy Optimisation Study (ATHOS), minimum inhibitory concentrations (MICs) were determined for cephalosporins alone and in combination with the β-lactamase inhibitors tazobactam, clavulanic acid and avibactam against third-generation cephalosporin-resistant Escherichia coli, Klebsiella spp. and Enterobacter spp. isolates collected in German hospitals. MIC50/90 values were 0.25–4 mg/L for cefepime/tazobactam, 0.25–2 mg/L for ceftazidime/avibactam, 0.125–0.5 mg/L for ceftaroline/avibactam, 0.5–4 mg/L for cefpodoxime/clavulanic acid and 0.25–1 mg/L for aztreonam/avibactam, depending on the underlying resistance mechanism and organism. Based on in vitro testing, β-lactam antibiotics play an important role in the treatment of infections due to β-lactamase-producing organisms.