Comparison of antimicrobial activity between ceftolozane-tazobactam and ceftazidime-avibactam against multidrug-resistant isolates of Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa

Objective: This study compared the activity of ceftolozane-tazobactam and ceftazidime-avibactam against 120 bacterial strains, including extended-spectrum beta-lactamase (ESBL) producers, carbapenem- resistant Enterobacteriaceae (CRE), and Pseudomonas aeruginosa, isolated from patients admitted to Cleveland Clinic Abu Dhabi, United Arab Emirates. Methods: In vitro susceptibility was tested using the Etest strip minimum inhibitory concentration (MIC) method, and PCR was used to characterize the carbapenemase enzymes produced by CRE strains. Results: All 29 ESBL isolates were susceptible to ceftazidime-avibactam (MIC50 0.125 mu g/ml), whereas all but one were susceptible to ceftolozane-tazobactam (MIC50 0.38 mu g/ml). Twenty-seven (45%) CRE isolates were susceptible to ceftazidime-avibactam (MIC50 >= 256 mu g/ml), whereas only six (10%) isolates were susceptible to ceftolozane-tazobactam (MIC50 >= 256 mu g/ml). Very few NDM-1 isolates were susceptible to ceftazidime-avibactam, whereas the majority of OXA-48 isolates were susceptible. Twenty-nine (94%) P. aeruginosa isolates were susceptible to ceftazidime-avibactam (MIC50 1.5 mu g/ml), whereas 30 (97%) isolates were susceptible to ceftolozane-tazobactam (MIC50 0.75 mu g/ml). Conclusions: Ceftolozane-tazobactam and ceftazidime-avibactam showed comparable activity against ESBL and P. aeruginosa, with ceftazidime-avibactam having lower MICs against ESBL isolates and ceftolozane-tazobactam having lower MICs against P. aeruginosa. Ceftazidime-avibactam showed better activity against all CRE isolates except for those carrying the NDM-1 enzyme. (C) 2017 The Authors. Published by Elsevier Ltd on behalf of International Society for Infectious Diseases.