Activity of Ceftolozane-Tazobactam Against Gram-Negative Isolates from Australia and New Zealand as part of the PACTS Surveillance 2016-2018

•Susceptibilities of Gram-negative isolates from Australia and New Zealand (2016-2018) were analyzed.•Susceptibility of P. aeruginosa to ceftolozane/tazobactam was 97.5%.•Susceptibility of Enterobacterales to ceftolozane/tazobactam was 96.5%.•Three Enterobacterales were carbapenem-resistant out of 1,693 isolates. : Ceftolozane-tazobactam (C-T) is an anti-pseudomonal cephalosporin combined with a well-described β-lactamase inhibitor. C-T has enhanced activity against Pseudomonas aeruginosa, and activity against Enterobacterales isolates that produce extended-spectrum β-lactamases (ESBL) or AmpC cephalosporinases. In this study, we analysed the susceptibility of Gram-negative isolates to C-T and comparators collected in Australia and New Zealand from 2016-2018 as part of The Program to Assess Ceftolozane-Tazobactam Susceptibility (PACTS) surveillance. : A total of 1,693 nonduplicate Enterobacterales and 435 P. aeruginosa isolates were collected prospectively from hospitalized patients in 6 medical centres in Australia and 2 in New Zealand. Susceptibilities (S) to C-T and comparators were determined using broth microdilution. EUCAST breakpoints were used. Isolates with multi-drug resistant (MDR), extensively drug resistant (XDR), extended spectrum β-lactamase non-carbapenem resistant (ESBL, non-CRE) phenotype, and CRE were analysed. : For P. aeruginosa, 97.5% were S to C-T while 89.9% were S to meropenem. According to EUCAST criteria, 86.4% were susceptible-increased exposure to piperacillin-tazobactam. MDR and XDR P. aeruginosa isolates had 76.7% and 65.4%S to C-T, respectively; 34.9% and 19.2%S to meropenem, respectively; 23.3% and 15.4% were susceptible-increased exposure to piperacillin-tazobactam, respectively. Meropenem (99.8%S), amikacin (99.1%S), and C-T (96.5%S) were the most active against Enterobacterales. Susceptibilities to C-T were 94.3% for ESBL, non-CRE phenotype and 78.4% for MDR isolates. Only 3 CRE and 5 XDR were identified. : These in vitro data indicate that C-T is a potent antimicrobial with activity against MDR and XDR P. aeruginosa, as well as ESBL, non-CRE phenotype isolates and MDR Enterobacterales.