656. Comparative Activity of Newer β-Lactam/β-Lactamase Inhibitor Combinations against <i>Pseudomonas aeruginosa</i> isolates from United States Medical Centers (2020-2021)

Abstract Background P. aeruginosa (PSA) is one of the most common Gram-negative organisms causing infections in hospitalized patients. Prompt administration an effective antimicrobial crucial for patients with systemic PSA infection. We evaluated vitro activity ceftazidime-avibactam (CAZ-AVI), ceftolozane-tazobactam (C-T), meropenem-vaborbactam (MEM-VAB), imipenem-relebactam (IMI-REL), and many comparator agents against contemporary isolates from US hospitals. Methods 3,184 were consecutively collected 71 medical centers 2020-2021 susceptibility tested by reference broth microdilution methods a monitoring laboratory (JMI Laboratories). FDA CLSI breakpoints applied. Results CAZ-AVI (97.0% susceptible [S]), C-T (98.0%S), IMI-REL (97.3%S), tobramycin (TOB; 96.4%S) active aggregate isolate collection retained good piperacillin-tazobactam- (PIP-TAZ) nonsusceptible (NS), MEM-NS, multidrug-resistant (MDR) (Table 1). All other antimicrobials showed limited PIP-TAZ-NS, MDR isolates. The infection types pneumonia (45.9%), skin structure (19.0%), urinary tract (UTI; 17.0%), bloodstream (11.7%); CAZ-AVI, C-T, consistent these types. Susceptibility to PIP-TAZ MEM lower among compared 2). remained 31.7% 52.5% C-T-NS IMI-REL-NS isolates, respectively. 54.7% 68.9% CAZ-AVI-NS respectively, 64.2% 64.8% NS Conclusion highly exhibited similar coverage large Cross resistance new β-lactamase inhibitor combinations varied markedly, indicating that all 3 should be clinical laboratory. These represent valuable therapeutic options treatment. Disclosures Helio S. Sader, MD, PhD, AbbVie: Grant/Research Support|Cidara: Support|Melinta: Support|Nabriva Therapeutics: Support|Pfizer: Support Rodrigo E. Mendes, Support|GSK: Support|Office Assistant Secretary Defense Health Affairs: Support|Shionogi: Support|Spero SJ Ryan Arends, Cecilia G. Carvalhaes, Mariana Castanheira, Support.