1081. Antimicrobial Activity of Ceftibuten-Avibactam against Clinical Isolates of <i>Enterobacterales</i> Producing Clinically Relevant Beta-Lactamases

Abstract Background Ceftibuten (CTB) is an oral cephalosporin active against Enterobacterales approved by the US Food and Drug Administration in 1995. Avibactam (AVI) is a potent inhibitor of extended-spectrum β-lactamases (ESBLs), serine carbapenemases and AmpC that can be administered orally. We evaluated the in vitro activity of CTB-AVI against molecularly characterized Enterobacterales that produced the most common β-lactamases (BLs) and assessed the AVI concentration to be combined with CTB for susceptibility testing. Methods The organism collection (n=71) included Enterobacterales producing ESBLs (28; CTX-M, SHV, and TEM), KPCs (8), MBLs (7; NDM, VIM, and IMP), AmpC derepressed (3), plasmid AmpC (3), OXA-48-like (2), and SME (2) as well as isolates with porin alterations (5) and wild-type organisms (13). Resistance mechanisms were evaluated by whole genome sequencing. MIC values were determined by broth microdilution of CTB with fixed concentrations (2, 4, and 8 mg/L) and ratios (1:1 and 2:1) of AVI. Results The fixed AVI concentration of 4 mg/L best separated CTB-AVI-susceptible from CTB-AVI-resistant isolates. CTB-AVI (fixed 4 mg/L) was very active against Enterobacterales producing ESBL (MIC50/90, 0.03/0.12 mg/L), including CTX-M-15 (MIC50/90, 0.03/0.12 mg/L), KPC (MIC50, 0.06 mg/L), derepressed AmpC (MIC range, 1-2 mg/L), plasmidic AmpC (MIC range, 0.12-0.5 mg/L), SME (MIC range, 0.06-0.12 mg/L), and OXA-48-like (MIC range, 0.5-4 mg/L), but it showed limited activity against MBL-producers (MIC50, &amp;gt;128 mg/L) and isolates with porin alterations (MIC50, 32 mg/L; Table). CTB was very active against SME-producers (MIC, 0.12-0.25 mg/L) and showed some activity against KPC-producers (MIC50, 4 mg/L; MIC range, 2-16 mg/L) and ESBL-producers (MIC50/90, 4/64 mg/L), but it exhibited very limited activity against MBL, AmpC derepressed, plasmidic AmpC, and OXA-48-like producers (MIC50 values of 128 to &amp;gt;128 mg/L). Conclusion CTB-AVI showed potent in vitro activity against Enterobacterales producing most clinically relevant BLs, including ESBLs, KPCs, OXA-48-like, and AmpC, for which limited oral treatment options are available. These in vitro results support further clinical development of CTB-AVI. Disclosures Helio S. Sader, MD, PhD, FIDSA, AbbVie (formerly Allergan) (Research Grant or Support)Basilea Pharmaceutica International, Ltd. (Research Grant or Support)Cipla Therapeutics (Research Grant or Support)Cipla USA Inc. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support, Contract no. HHSO100201600002C)Melinta Therapeutics, LLC (Research Grant or Support)Nabriva Therapeutics (Research Grant or Support)Pfizer, Inc. (Research Grant or Support)Shionogi (Research Grant or Support)Spero Therapeutics (Research Grant or Support) Jill Lindley, Bravos Biosciences (Research Grant or Support)ContraFect Corporation (Research Grant or Support)Pfizer, Inc. (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Lalitagauri M. Deshpande, PhD, AbbVie (formerly Allergan) (Research Grant or Support)Pfizer, Inc. (Research Grant or Support) Timothy B. Doyle, AbbVie (formerly Allergan) (Research Grant or Support)Bravos Biosciences (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Pfizer, Inc. (Research Grant or Support)Shionogi (Research Grant or Support)Spero Therapeutics (Research Grant or Support) Mariana Castanheira, PhD, AbbVie (formerly Allergan) (Research Grant or Support)Bravos Biosciences (Research Grant or Support)Cidara Therapeutics, Inc. (Research Grant or Support)Cipla Therapeutics (Research Grant or Support)Cipla USA Inc. (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, LLC (Research Grant or Support)Pfizer, Inc. (Research Grant or Support)Qpex Biopharma (Research Grant or Support)Shionogi (Research Grant or Support)Spero Therapeutics (Research Grant or Support) Mariana Castanheira, PhD, Affinity Biosensors (Individual(s) Involved: Self): Research Grant or Support; Allergan (Individual(s) Involved: Self): Research Grant or Support; Amicrobe, Inc (Individual(s) Involved: Self): Research Grant or Support; Amplyx Pharma (Individual(s) Involved: Self): Research Grant or Support; Artugen Therapeutics USA, Inc. (Individual(s) Involved: Self): Research Grant or Support; Astellas (Individual(s) Involved: Self): Research Grant or Support; Basilea (Individual(s) Involved: Self): Research Grant or Support; Beth Israel Deaconess Medical Center (Individual(s) Involved: Self): Research Grant or Support; BIDMC (Individual(s) Involved: Self): Research Grant or Support; bioMerieux Inc. (Individual(s) Involved: Self): Research Grant or Support; BioVersys Ag (Individual(s) Involved: Self): Research Grant or Support; Bugworks (Individual(s) Involved: Self): Research Grant or Support; Cidara (Individual(s) Involved: Self): Research Grant or Support; Cipla (Individual(s) Involved: Self): Research Grant or Support; Contrafect (Individual(s) Involved: Self): Research Grant or Support; Cormedix (Individual(s) Involved: Self): Research Grant or Support; Crestone, Inc. (Individual(s) Involved: Self): Research Grant or Support; Curza (Individual(s) Involved: Self): Research Grant or Support; CXC7 (Individual(s) Involved: Self): Research Grant or Support; Entasis (Individual(s) Involved: Self): Research Grant or Support; Fedora Pharmaceutical (Individual(s) Involved: Self): Research Grant or Support; Fimbrion Therapeutics (Individual(s) Involved: Self): Research Grant or Support; Fox Chase (Individual(s) Involved: Self): Research Grant or Support; GlaxoSmithKline (Individual(s) Involved: Self): Research Grant or Support; Guardian Therapeutics (Individual(s) Involved: Self): Research Grant or Support; Hardy Diagnostics (Individual(s) Involved: Self): Research Grant or Support; IHMA (Individual(s) Involved: Self): Research Grant or Support; Janssen Research &amp; Development (Individual(s) Involved: Self): Research Grant or Support; Johnson &amp; Johnson (Individual(s) Involved: Self): Research Grant or Support; Kaleido Biosceinces (Individual(s) Involved: Self): Research Grant or Support; KBP Biosciences (Individual(s) Involved: Self): Research Grant or Support; Luminex (Individual(s) Involved: Self): Research Grant or Support; Matrivax (Individual(s) Involved: Self): Research Grant or Support; Mayo Clinic (Individual(s) Involved: Self): Research Grant or Support; Medpace (Individual(s) Involved: Self): Research Grant or Support; Meiji Seika Pharma Co., Ltd. (Individual(s) Involved: Self): Research Grant or Support; Melinta (Individual(s) Involved: Self): Research Grant or Support; Menarini (Individual(s) Involved: Self): Research Grant or Support; Merck (Individual(s) Involved: Self): Research Grant or Support; Meridian Bioscience Inc. (Individual(s) Involved: Self): Research Grant or Support; Micromyx (Individual(s) Involved: Self): Research Grant or Support; MicuRx (Individual(s) Involved: Self): Research Grant or Support; N8 Medical (Individual(s) Involved: Self): Research Grant or Support; Nabriva (Individual(s) Involved: Self): Research Grant or Support; National Institutes of Health (Individual(s) Involved: Self): Research Grant or Support; National University of Singapore (Individual(s) Involved: Self): Research Grant or Support; North Bristol NHS Trust (Individual(s) Involved: Self): Research Grant or Support; Novome Biotechnologies (Individual(s) Involved: Self): Research Grant or Support; Paratek (Individual(s) Involved: Self): Research Grant or Support; Pfizer (Individual(s) Involved: Self): Research Grant or Support; Prokaryotics Inc. (Individual(s) Involved: Self): Research Grant or Support; QPEX Biopharma (Individual(s) Involved: Self): Research Grant or Support; Rhode Island Hospital (Individual(s) Involved: Self): Research Grant or Support; RIHML (Individual(s) Involved: Self): Research Grant or Support; Roche (Individual(s) Involved: Self): Research Grant or Support; Roivant (Individual(s) Involved: Self): Research Grant or Support; Salvat (Individual(s) Involved: Self): Research Grant or Support; Scynexis (Individual(s) Involved: Self): Research Grant or Support; SeLux Diagnostics (Individual(s) Involved: Self): Research Grant or Support; Shionogi (Individual(s) Involved: Self): Research Grant or Support; Specific Diagnostics (Individual(s) Involved: Self): Research Grant or Support; Spero (Individual(s) Involved: Self): Research Grant or Support; SuperTrans Medical LT (Individual(s) Involved: Self): Research Grant or Support; T2 Biosystems (Individual(s) Involved: Self): Research Grant or Support; The University of Queensland (Individual(s) Involved: Self): Research Grant or Support; Thermo Fisher Scientific (Individual(s) Involved: Self): Research Grant or Support; Tufts Medical Center (Individual(s) Involved: Self): Research Grant or Support; Universite de Sherbrooke (Individual(s) Involved: Self): Research Grant or Support; University of Iowa (Individual(s) Involved: Self): Research Grant or Support; University of Iowa Hospitals and Clinics (Individual(s) Involved: Self): Research Grant or Support; University of Wisconsin (Indivi

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