1252. In Vitro Activity of Aztreonam-Avibactam and Comparator Agents Against Enterobacterales from Patients with Bloodstream Infections collected during the ATLAS Global Surveillance Program, 2015-2019

BACKGROUND: Treatment options for β-lactamase-producing Enterobacterales are limited, particularly for infections caused by metallo-β-lactamase (MBL)-producing strains. The β-lactam/non-β-lactam β-lactamase inhibitor combination aztreonam-avibactam (ATM-AVI) is active in vitro against Enterobacterales isolates carrying MBLs, including those co-producing β-lactamases of Class A, C, and some class D enzymes. This study evaluated the in vitro activity of ATM-AVI and comparators against Enterobacterales isolates collected in 2015-2019 from patients with bloodstream infections (BSI) as part of the ATLAS program. METHODS: Non-duplicate clinical isolates were collected in 53 countries in Europe, Latin America, Asia/Pacific (excluding mainland China and India), and Middle East/Africa. Susceptibility testing was performed by CLSI broth microdilution and interpreted using CLSI 2021 and FDA (tigecycline) breakpoints. ATM-AVI was tested at a fixed concentration of 4 µg/mL AVI. MDR was defined as resistant (R) to ≥3 of 7 sentinel drugs: amikacin, aztreonam, cefepime, colistin, levofloxacin, meropenem, and piperacillin-tazobactam. PCR and sequencing were used to determine the β-lactamase genes present in all isolates with meropenem MIC >1 µg/mL, and Escherichia coli, Klebsiella spp. and Proteus mirabilis phenotypically positive for ESBL activity (2015) or with aztreonam or ceftazidime MIC >1 µg/mL (2016-2019). RESULTS: ATM-AVI was active in vitro against Enterobacterales isolates from BSI (MIC(90), 0.12 µg/mL), with 99.97% of isolates inhibited by ≤8 µg/mL of ATM-AVI, including 100% of isolates that produced MBLs. ATM-AVI tested with MIC(90) values of 0.5 µg/mL against subsets of cefepime-nonsusceptible (NS), meropenem-NS, amikacin-NS, colistin-resistant, and MBL-positive Enterobacterales (Table). The tested β-lactam comparators showed susceptibility of < 79% against these subsets of resistant isolates. Results Table [Image: see text] CONCLUSION: Based on MIC(90) values, ATM-AVI was the most potent agent tested against drug-resistant and MBL-positive subsets of Enterobacterales collected from BSI. The promising in vitro activity of ATM-AVI warrants further development of this combination for treatment of BSI caused by drug-resistant Enterobacterales. DISCLOSURES: Sibylle Lob, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor) Francis Arhin, PhD, Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Independent Contractor)