In vitro activity of ceftolozane/tazobactam against Gram-negative bacilli isolated from pediatric patients: Results from the Study for Monitoring Antimicrobial Resistance Trends (SMART) 2017-2021, China

Objectives: Ceftolozane-tazobactam (C/T) is a combination of a cephalosporin and a beta-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 paediatric patients. Methods: From 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. Results: GNB isolates were obtained from paediatric 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 beta-lactam antibiotics 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 beta-lactam antibiotics tested, except for ceftazidimeavibactam (91.2%). Conclusion: GNBs collected from paediatric patients in China showed a high susceptibility to C/T making this drug combination an effective choice for treating the paediatric population, especially those infected with P. aeruginosa .