P-1478. Assessment of Beta-lactam Susceptibility Profiles in <i>Pseudomonas aeruginosa</i>: A Comprehensive Analysis at an Academic Medical Center

Abstract Background Pseudomonas aeruginosa is one of the most difficult bacterial pathogens to treat. As beta-lactams remain the most prescribed class of antimicrobials to treat P. aeruginosa infections, the objective of this study was to describe susceptibility profiles of first line beta-lactam antimicrobials against P. aeruginosa at our academic medical center. Methods All non-duplicate P. aeruginosa isolates from 2021-2023 were analyzed. First line beta-lactams evaluated included aztreonam (AZT), ceftazidime (CAZ), cefepime (CFP), piperacillin/tazobactam (PTZ), meropenem (MEM) as well as newer beta-lactams ceftolozane-tazobactam (C/T), and ceftazidime/avibactam (C/A). Susceptibility testing was performed with the BD Phoenix™ automated system or E-test. Data obtained for each patient included culture date, source of infection, hospital location, and MIC. Each MIC was categorized as susceptible, intermediate, or resistant based on 2024 CLSI MIC breakpoints. Results Overall susceptibility rates for each beta-lactam for 1177 isolates were as follows: AZT (75%), CAZ (82%), CFP (83%), PTZ (79%), MEM (84%), C/T (99%), and C/A (99%). Moreover, 70% of P. aeruginosa strains were susceptible to all first line beta-lactams tested, while 25% displayed non-susceptibility to at least 1 first line beta-lactam, and 5% exhibited non-susceptibility to all first line beta-lactams tested. Among strains non-susceptible to at least 1 first line beta-lactam, the majority (37%) exhibited non-susceptibility to only 1 beta-lactam, while 20% and 19% displayed non-susceptibility to 2 or 3 beta-lactams, respectively. Additionally, 25% demonstrated non-susceptibility to 4 beta-lactams. Finally, respiratory isolates consistently displayed the highest incidence of non-susceptibility for each beta-lactam compared to blood, urine, wound, and miscellaneous body sites. Conclusion This study highlights the variable susceptibility of first-line beta-lactam antimicrobials against P. aeruginosa infections. These findings stress the importance of customized treatment strategies, surveillance for evolving resistance, and considering newer beta-lactams such as ceftolozane-tazobactam and ceftazidime-avibactam, alongside prudent antibiotic utilization in clinical practice. Disclosures All Authors: No reported disclosures