Pseudomonas aeruginosa is a pathogen that causes severe infections that are difficult to treat, as this bacterium can express multiple resistance mechanisms, in addition to its intrinsically limited susceptibility to many antibiotics. In this study, the in vitro activity of ceftazidime-avibactam was evaluated against clinical isolates of P. aeruginosa, both carbapenemase-producing and non-producing, collected as part of the global ATLAS surveillance program.

A total of 1239 non-duplicate P. aeruginosa isolates were evaluated, collected from different infection sites in hospitals across Brazil between 2018 and 2023. Susceptibility testing was performed using broth microdilution. The antimicrobial susceptibility profile was analyzed according to the breakpoints established by BrCAST (2025). The search for carbapenemase-encoding genes was performed by PCR followed by sequencing. Results Ceftazidime-avibactam (90.0% susceptible; MIC50/90, 2.0/8.0 mg/L) and colistin (99.8% susceptible; MIC50/90, 1.0/1.0 mg/L) were the antibiotics with the best in vitro activity. Approximately 70% of isolates tested for imipenem, cefepime, ceftazidime, and piperacillin-tazobactam were classified as susceptible with increased exposure, according to BrCAST criteria (range 68.7% to 74.5%). Susceptibility to ceftolozane-tazobactam was 84.3% (MIC50/90, 1.0/32.0 mg/L), but this antibiotic was evaluated in only 949/1239 isolates. Resistance gene screening was performed on 153 isolates, of which 17 (11%) were blaKPC-2 producers (4 also coproduced blaGES-1). The beta-lactamases found in 22 (18%) of the 123 ceftazidime-avibactam resistant P. aeruginosa isolates were: NDM-1 (n = 5), KPC-2 (n = 5), VIM-2 (n = 5), SPM-1 (n = 1), SPM-1+GES-1 (n = 1), IMP-16 (n = 1), IMP-56 (n = 1), KPC-2+GES-1 (n = 1), NDM-1+VEB-9 (n = 1), and NDM-1+VEB-14 (n = 1).

The results demonstrated that both ceftazidime-avibactam and ceftolozane-tazobactam maintain excellent in vitro activity (> 80%) against clinical isolates of P. aeruginosa. Although the presence of carbapenemases was relatively low among the isolates studied, ceftazidime-avibactam was 5 times more potent (MIC90) compared to ceftolozane-tazobactam, which may be partly explained by the presence of these beta-lactamases identified in the evaluated isolates.