Evaluation of the In vitro Activity of Ceftazidime-Avibactam and Ceftolozane-Tazobactam against Ceftazidime-Resistant Pseudomonas aeruginosa Isolates

Introduction: This study aimed to assess the in vitro efficacy of ceftazidime/avibactam (CZA) and ceftolozane/tazobactam (C/T) against ceftazidime resistant Pseudomonas aeruginosa clinical isolates from Samsun Training and Research Hospital. Materials and Methods: A total of 52 unique patient isolates of ceftazidime resistant P. aeruginosa were included in this study. Identification and antimicrobial susceptibilities of the strains were performed using a VITEK 2 (R) automated system. The efficacy of CZA and C/T were determined by the gradient diffusion method (Liofilchem MIC strip test, Italy). We used the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guidelines for Minimal Inhibitory Concentration interpretation. Results: Among these 52 strains, 49 (94.2%) were susceptible to CZA and 51 (98.1%) to C/T. Both CZA and C/T had better activity than any one of the 3 anti-pseudomonal beta-lactams. Although the susceptibility rates of isolates to CZA and C/T were similar, according to MIC50 values C/T (MIC(50 )1 mu g/mL) was 2-fold more potent than CZA (MIC50, 2 mu g/mL). Conclusion: CZA and C/T showed good activity against ceftazidime-resistant and/or carbapenem-resistant P. aeruginosa isolates and may serve as therapeutic options for infections caused by these organisms. However, further in vitro and in vivo studies are needed to assess the effectiveness of these new antimicrobials against multiple drug resistant P. aeruginosa isolates.