In Vitro Activity of Ceftazidime-Avibactam Against Carbapenem-Resistant Enterobacterales: A Prospective Study from a Tertiary Care Centre in Patna, India

Abstract

Background: Carbapenem-resistant Enterobacterales (CRE) represent a critical therapeutic challenge with limited treatment options. Ceftazidime-avibactam (CZA), a novel β-lactam/β-lactamase inhibitor combination, has shown promising in vitro activity against CRE. This study aimed to evaluate the in vitro susceptibility of CZA against CRE isolates at a tertiary care hospital in eastern India.
Methods: In this prospective cross-sectional study conducted at the Department of Microbiology, IGIMS, Patna, 450 non-duplicate CRE isolates were collected from various clinical samples over nine months. Species identification was performed by conventional biochemical methods and MALDI-TOF MS. Carbapenem resistance was confirmed by Kirby-Bauer disc diffusion (KBDD) and VITEK-2. CZA susceptibility was tested by KBDD and E-test and interpreted per CLSI 2024 guidelines.
Results: Of 450 clinical isolates, 180 (40%) were CRE. Klebsiella pneumoniae (49.4%) was the predominant species, followed by Escherichia coli (25.6%) and Enterobacter cloacae (12.8%). The ICU contributed the highest proportion of CRE (30.6%). By disc diffusion, 63.3% of CRE isolates were susceptible to CZA. E-test MIC analysis confirmed susceptibility in 65.0% of isolates (MIC90 = 8 mg/L). Overall categorical agreement between the two methods was 92.2%. Among K. pneumoniae isolates, CZA susceptibility was 58.4%, while E. coli showed the highest susceptibility (69.6%).
Conclusion: CZA demonstrated clinically significant in vitro activity against CRE isolates, with susceptibility rates exceeding 60%. These findings support CZA as a viable therapeutic option for CRE infections in the Indian clinical setting. Routine susceptibility testing of CZA is recommended for CRE isolates to guide optimal treatment decisions.