1567. In Vitro Activity of Aztreonam-Avibactam and Comparator Agents Against Multidrug-Resistant Enterobacterales Collected Globally as Part of the ATLAS Surveillance Program, 2016-2018

BACKGROUND: Avibactam (AVI) is a serine-β-lactamase inhibitor in development with aztreonam (ATM) for treatment of infections caused by drug-resistant Enterobacterales (Ent), especially carbapenem-resistant isolates co-producing serine- and metallo-β-lactamases (MBL), which are often resistant to agents from multiple drug classes. This study evaluated the in vitro activity of ATM-AVI and comparators against Ent collected globally as part of the Antimicrobial Testing Leadership and Surveillance (ATLAS) program. METHODS: 44,671 non-duplicate clinical isolates were collected in 2016-2018 in 52 countries in Europe, Asia/Pacific (excluding China and India), Middle East/Africa, and Latin America. Susceptibility testing was performed by CLSI broth microdilution and interpreted using CLSI 2020 and FDA (tigecycline) breakpoints. ATM-AVI was tested at a fixed concentration of 4 µg/mL AVI. Drug-resistant phenotypes were defined as: multidrug resistant (MDR), resistant (R) to ≥3 of 7 sentinel agents (amikacin [AMK], ATM, cefepime [FEP], colistin [CST], levofloxacin [LVX], meropenem [MEM], piperacillin-tazobactam [TZP]); extensively drug resistant (XDR), susceptible to ≤2 sentinel agents; and pandrug resistant (PDR), non-susceptible to all sentinel agents. Isolates with MEM MIC >1 µg/mL were screened for β-lactamase genes by PCR and sequencing. RESULTS: 14.9%, 4.3%, 3.7%, 1.3%, and 0.3% of Ent collected globally were MDR, XDR, MEM-R, MBL-positive, and PDR, respectively. ATM-AVI tested with MIC(90) values of 0.12 µg/mL against all Ent and 0.5 µg/mL against subsets of resistant isolates (Table). On the regional level, similar values were observed against all (MIC(90), 0.12 µg/mL) and resistant isolates (MIC(90), 0.25-1 µg/mL) (not shown). The tested comparators, excluding TGC, showed percentages of susceptibility < 90% against regional and global subsets of resistant isolates. 99.97% (44658 of 44671) Ent, including all MBL-positive and PDR isolates, were inhibited by ≤8 µg/mL of ATM-AVI. Table [Image: see text] CONCLUSION: Based on MIC(90) values, ATM-AVI demonstrated potent in vitro activity against resistant and MBL-positive subsets of Ent collected globally. ATM-AVI could be an effective therapy for difficult-to-treat infections caused by drug-resistant Ent. DISCLOSURES: Krystyna Kazmierczak, PhD, IHMA (Employee)Pfizer, Inc. (Consultant) Francis Arhin, PhD, Pfizer, Inc. (Employee) Greg Stone, PhD, AztraZeneca (Shareholder, Former Employee)Pfizer, Inc. (Employee) Daniel F. Sahm, PhD, IHMA (Employee)Pfizer, Inc. (Consultant)Shionogi & Co., Ltd. (Independent Contractor)