(1453) Antimicrobial Susceptibility of Pseudomonas aeruginosa From Elderly Patients in the ICU

Introduction: Prompt administration of an effective antimicrobial is crucial for patients with systemic P. aeruginosa (PSA) infection. We evaluated the in vitro activity of ceftazidime-avibactam (CAZ-AVI), ceftolozane-tazobactam (C-T), imipenem-relebactam (IMI-REL), and many comparator agents against contemporary PSA isolates from United States (US) medical centers.

Methods: Bacterial isolates were consecutively collected from 69 US medical centers in 2021-2023 and susceptibility tested by reference broth microdilution methods in the monitoring laboratory. Results for PSA isolates from intensive care unit (ICU) elderly patients (≥65 years old [y-o]; n=593) were compared to those of non-ICU elderly patients (n=1,279) and ICU nonelderly patients (≤64 y-o; n=944).

Results: The most active agents against PSA from ICU elderly patients were IMI-REL (97.5% susceptible [S]), CAZ-AVI (97.0%S), C-T (97.0%S), tobramycin (TOB; 92.2%S), and cefepime (FEP; 82.5%S). CAZ-AVI, C-T, and IMI-REL were also highly active against PSA from non-ICU elderly patients (97.5% to 98.7%S) and nonelderly patients from ICU (96.3% to 97.5%S). Among isolates recovered from elderly patients, lower susceptibility for ICU isolates compared to non-ICU isolates was observed for piperacillin-tazobactam (PIP-TAZ; 74.5% [ICU] vs. 84.7% [non-ICU]), meropenem (MEM; 76.7% vs. 87.7%), imipenem (77.9% vs. 86.1%), ceftazidime (78.8% vs. 87.1%), and cefepime (82.5% vs. 88.8%). Susceptibility for these agents were also lower among isolates from the ICU elderly patients compared to ICU nonelderly patients, especially for MEM (76.7% vs. 80.0%) and PIP-TAZ (74.5% vs. 76.7%). In general, CAZ-AVI was active against 49.4% of IMI-REL-non-S and 33.6% of C-T-non-S isolates, C-T was active against 53.4% of IMI-REL-non-S and 42.8% of CAZ-AVI-non-S isolates, and IMI-REL was active against 68.5% of CAZ-AVI-non-S and 66.9% of C-T-non-S isolates.

Conclusions: CAZ-AVI, C-T, and IMI-REL were highly active and exhibited similar coverage against a large contemporary collection of PSA isolates from elderly patients. Cross-resistance among these new β-lactamase inhibitor combinations varied markedly, indicating that all 3 should be tested in the clinical laboratory and available for clinical use.