Antibacterial activity of enmetazobactam against Acinetobacter spp.: a molecular dissection of mechanism of action and resistance determinants

  • Antimicrob Agents Chemother. 2025 Dec 22:e0120625. doi: 10.1128/aac.01206-25.
Gabriela-Alejandra Báez-Barroso  #  1 ,  Arianna Rodríguez-Coello  #  1 ,  Juan Carlos Vázquez-Ucha  #  1  2 ,  Silvia López-Argüello  2  3 ,  Michelle Outeda-García  1  2 ,  Lucía González-Pinto  1  2 ,  Andrea García-Pose  1 ,  Paula Guijarro-Sánchez  1 ,  Isaac Alonso-García  1  2 ,  Emilio Lence  4  5 ,  Concepción González-Bello  4 ,  Antonio Oliver  2  3 ,  Jorge Arca-Suárez  1  2 ,  Bartolome Moya  2  3 ,  Germán Bou  #  1  2  6 ,  Alejandro Beceiro  #  1  2 ,  Spanish National Acinetobacter spp. 2020 Study Group
Affiliations
  • 1. Servicio de Microbiología and Instituto de Investigación Biomédica A Coruña (INIBIC), Complexo Hospitalario Universitario A Coruña (CHUAC), A Coruña, Spain.
  • 2. Ciber de Enfermedades Infecciosas (CIBERINFEC), Instituto de Salud Carlos III, Madrid, Spain.
  • 3. Servicio de Microbiología and Unidad de Investigación, Hospital Universitario Son Espases, Health Research Institute of the Balearic Islands (IdISBa), Palma, Spain.
  • 4. Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CiQUS), Departamento de Química Orgánica, Universidade de Santiago de Compostela, Santiago de Compostela, Spain.
  • 5. Departamento de Química Orgánica, Facultad de Ciencias, Universidad de Valladolid, Valladolid, Spain.
  • 6. Departamento de Fisioterapia, Medicina y Ciencias Biomédicas, Universidad de A Coruña, A Coruña, Spain.
  • # Contributed equally.
PMID: 41427713 DOI: 10.1128/aac.01206-25
Abstract

The persistence of multidrug-resistant Acinetobacter baumannii remains a clinical challenge. Cefepime/enmetazobactam is a novel combination with demonstrated activity against extended-spectrum β-lactamase-producing Enterobacterales, but its activity against Acinetobacter has not yet been thoroughly explored. We aimed to assess its activity against Acinetobacter spp., including multidrug-resistant strains producing carbapenem-hydrolyzing class D β-lactamases (CHDLs). We analyzed 208 clinical isolates of Acinetobacter spp., including 67 carbapenem-resistant Acinetobacter baumannii (CRAB). Antibiotic susceptibility testing was conducted with cefepime, sulbactam, and imipenem, alone and in combination with enmetazobactam; the latter was also tested individually. Additionally, MICs of enmetazobactam/durlobactam and sulbactam/durlobactam were determined for CRAB and CHDL-producing A. baumannii ATCC 17978 transformants. PBP binding assays (IC₅₀), molecular docking, simulation studies with the enmetazobactam/OXA-23 adduct, hydrolysis kinetics (kcat, Km), and OXA-23 inhibition assays (IC₅₀, koff, t₁/₂) were performed to elucidate the mechanism of enmetazobactam and detect reduced susceptibility. Enmetazobactam showed high intrinsic activity against Acinetobacter spp., displaying reduced MICs against carbapenem-susceptible isolates. MIC50/90 of the enmetazobactam/durlobactam combination was 2/2 mg/L for CHDL-producing A. baumannii. Enmetazobactam exhibited bactericidal activity comparable to sulbactam. Binding assays revealed that the antimicrobial activity is driven by selective affinity for PBP2 (IC₅₀ 3.6 mg/L) and PBP3 (IC₅₀ 4.2 mg/L). OXA-23 readily inactivated enmetazobactam, confirming the major role of CHDLs in resistance to enmetazobactam, via substrate-assisted de-acylation. This study evidences the potent antimicrobial activity of enmetazobactam against A. baumannii via inhibition of PBP2 and PBP3. Its combination with new OXA-type inhibitors (e.g., durlobactam) represents a potential therapeutic alternative for multidrug-resistant A. baumannii.

Keywords
Acinetobacter baumannii; Acinetobacter spp.; PBPs; antimicrobial resistance; carbapenem-hydrolyzing class D β-lactamases; cefepime/enmetazobactam; durlobactam; sulbactam.
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