Trends in Pseudomonas aeruginosa In Vitro Susceptibility to Ceftolozane/Tazobactam in Latin America: SMART Surveillance Program, 2016–2024

<b>Objectives</b>: To describe annual trends in the susceptibility of clinical isolates of <i>Pseudomonas aeruginosa</i> from Latin America to ceftolozane/tazobactam. <b>Methods</b>: The Study for Monitoring Antimicrobial Resistance Trends (SMART) surveillance program collected 10,188 <i>P. aeruginosa</i> isolates from 57 unique clinical sites in 12 Latin American countries from 2016 to 2024. MICs were determined by reference broth microdilution testing and interpreted using 2025 CLSI M100 breakpoints. <b>Results</b>: Overall, 86.3% of clinical isolates of <i>P. aeruginosa</i> collected in Latin America were susceptible to ceftolozane/tazobactam, including 45.5% of multidrug-resistant (MDR) isolates. From 2016 to 2024, annual percent susceptible values for ceftolozane/tazobactam ranged from 84.9% (2016, <i>n</i> = 779) to 89.2% (2023, <i>n</i> = 1144), with a statistically significant linear trend for increasing susceptibility (<i>p</i> = 0.024; Cochran-Armitage test for trend). However, limiting analysis solely to the 14 clinical sites, from six countries, that participated in each of the nine years (<i>n</i> = 4565) indicated that the annual percent susceptible values for ceftolozane/tazobactam remained unchanged from 2016 (82.6%) to 2024 (83.9%) (<i>p</i> = 0.367; percent susceptible value range, 82.6 to 89.1%). Every year, from 2016 to 2024, all <i>P. aeruginosa</i> isolates from pediatric patients (<18 years of age) were consistently more susceptible to ceftolozane/tazobactam than those from adult patients (90.3 to 95.0%/year versus 83.3 to 88.6%/year, respectively). Significant variation (<i>p</i> < 0.05) in annual ceftolozane/tazobactam percent susceptible values was not observed for isolates from blood, intra-abdominal, and respiratory tract sources, while isolates from urine showed a trend of increasing ceftolozane/tazobactam susceptibility from 73.1% (2018, <i>n</i> = 145) to 90.6% (2023, <i>n</i> = 117) (<i>p</i> < 0.0001). Among individual countries that participated each year, <i>P. aeruginosa</i> isolates from all except Guatemala displayed stable or increasing rates of susceptibility to ceftolozane/tazobactam. <b>Conclusions</b>: Since it was first tested by the SMART program in 2016, and for 8 years thereafter, the in vitro activity of ceftolozane/tazobactam has remained consistent against clinical isolates of <i>P. aeruginosa</i> from the Latin American region (overall, 86.3% susceptible), with limited resistance development restricted to specific clinical sites.