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

## TL;DR

This study tracks how well a drug called ceftolozane/tazobactam works against a common infection-causing bacteria in Latin America from 2016 to 2024.

## Contribution

The study provides the first detailed 8-year surveillance of ceftolozane/tazobactam susceptibility trends in Latin America against Pseudomonas aeruginosa.

## Key findings

- Overall, 86.3% of Pseudomonas aeruginosa isolates in Latin America were susceptible to ceftolozane/tazobactam.
- Pediatric isolates showed consistently higher susceptibility compared to adult isolates each year.
- Urine isolates showed a significant increase in susceptibility from 73.1% in 2018 to 90.6% in 2023.

## Abstract

Objectives: To describe annual trends in the susceptibility of clinical isolates of Pseudomonas aeruginosa from Latin America to ceftolozane/tazobactam. Methods: The Study for Monitoring Antimicrobial Resistance Trends (SMART) surveillance program collected 10,188 P. aeruginosa 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. Results: Overall, 86.3% of clinical isolates of P. aeruginosa 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, n = 779) to 89.2% (2023, n = 1144), with a statistically significant linear trend for increasing susceptibility (p = 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 (n = 4565) indicated that the annual percent susceptible values for ceftolozane/tazobactam remained unchanged from 2016 (82.6%) to 2024 (83.9%) (p = 0.367; percent susceptible value range, 82.6 to 89.1%). Every year, from 2016 to 2024, all P. aeruginosa 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 (p < 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, n = 145) to 90.6% (2023, n = 117) (p < 0.0001). Among individual countries that participated each year, P. aeruginosa isolates from all except Guatemala displayed stable or increasing rates of susceptibility to ceftolozane/tazobactam. Conclusions: 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 P. aeruginosa from the Latin American region (overall, 86.3% susceptible), with limited resistance development restricted to specific clinical sites.