In-vitro activity of ceftolozane/tazobactam against Pseudomonas aeruginosa collected in the Study for Monitoring Antimicrobial Resistance Trends (SMART) between 2016 and 2019 in China

Ceftolozane/tazobactam (an antipseudomonal cephalosporin) in combination with a well-established β-lactamase inhibitor has not been approved to date in clinical practice in China. The aim of this study was to evaluate the in-vitro activity of ceftolozane/tazobactam and comparator agents against Pseudomonas aeruginosa with various resistance patterns. P. aeruginosa (n=2178) specimens were collected from multiple sources in seven geographic regions of China between 2016 and 2019. All isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and minimum inhibitory concentrations of various antimicrobial agents (ceftolozane/tazobactam, amikacin, tobramycin, ceftazidime, cefepime, colistin, levofloxacin, aztreonam, meropenem, imipenem and piperacillin/tazobactam) were determined using the Clinical and Laboratory Standards Institute's broth microdilution method. P. aeruginosa demonstrated considerably high rates of multi-drug resistance (MDR, 57.3%), extensive drug resistance (XDR, 43.5%) and difficult-to-treat resistance (DTR, 16.8%). The overall susceptibility of P. aeruginosa to ceftolozane/tazobactam was 81.9%, and ceftolozane/tazobactam showed diverse activity against the three resistant subsets, ranging from 28.5% against DTR P. aeruginosa to 68.9% against MDR P. aeruginosa. P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa derived from the East (Jiangzhe area) region maintained significantly lower susceptibility to ceftolozane/tazobactam compared with P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa from other regions. The susceptibility rates of P. aeruginosa isolated from diverse sources to ceftolozane/tazobactam were similar to isolates from bloodstream infections, with the highest being 88.6%. Compared with other antimicrobial agents, ceftolozane/tazobactam was more active than the β-lactams tested but was slightly less active than amikacin. Amikacin demonstrated the best activity against P. aeruginosa and the three resistant subsets. Ceftolozane/tazobactam demonstrated considerable in-vitro activity against P. aeruginosa, MDR P. aeruginosa, XDR P. aeruginosa and DTR P. aeruginosa, indicating that it could be an optional therapeutic agent against P. aeruginosa.