ObjectivesCeftolozane-tazobactam (C/T) is a combination of a cephalosporin and a β-lactamase inhibitor with activity against Gram-negative bacilli (GNB). The study aims were to evaluate the activity of C/T in vitro vs. comparators against clinical GNB isolated from Chinese pediatric patients. MethodsFrom 2017-2021, 660 GNB isolates were collected from 20 hospitals across China. The minimum inhibitory concentrations were tested using a Trek Diagnostic System (Thermo Fisher Scientific). Susceptibility was determined by CLSI broth microdilution and the results were interpreted according to CLSI M100 (2021) breakpoints. ResultsGNB isolates were obtained from pediatric patients < 18 years old, mainly from the bloodstream (n=146), intraperitoneal cavity (n=138), lower respiratory (n=278) and urinary tract (n=96). Overall, C/T was active against 76.6% of 436 Enterobacterales, with a descending susceptibility rate of 100.0% to S. marcescens, 92.2% to E. coli, 83.3% to K. oxytoca, 66.7% to K. aerogenes, 66.7% to P. mirabilis, 58.6% to K. pneumoniae and 57.1% to E. cloacae. The susceptibility of P. aeruginosa to C/T was 89.4%, which was the highest among the β-lactams and was second only to amikacin (92.9%). Isolates of respiratory tract infection (RTI) derived P. aeruginosa were highly susceptible (93.8%) to C/T, while < 75% of isolates of RTI derived P. aeruginosa were susceptible to the other β-lactams tested, except for ceftazidime-avibactam (91.2%). ConclusionGNBs collected from pediatric patients in China showed a high susceptibility to C/T making this drug combination an effective choice for treating the pediatric population, especially those infected with P. aeruginosa.