Two-year antimicrobial susceptibility trends of Escherichia coli in a tertiary care centre: A retrospective analysis

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Background: Escherichia coli continues to be a leading pathogen responsible for a wide range of infections, from uncomplicated urinary tract infections to severe bloodstream infections. The growing burden of antimicrobial resistance makes periodic local surveillance essential for guiding empirical therapy.Materials and Methods: A retrospective analysis of all non-duplicate E.coli isolates collected at Chettinad Hospital and Research Institute between January 2024 and September 2025 was carried out. Kirby-Bauer disk diffusion antibiotic susceptibility testing data was retrieved and interpreted according to CLSI guidelines. A total of 15 antibiotics across six drug classes were tested. Data was analysed for annual trends and stratified by specimen type.Results: Among 24,683 samples processed, carbapenems remained the most reliable agents overall, with meropenem showing 89.5% susceptibility and imipenem 85.9%. For urinary isolates, fosfomycin (92.0%) and nitrofurantoin (82.0%) retained excellent activity. Overall mean susceptibility across all antibiotics increased marginally from 55.2% in 2024 to 56.1% in 2025. However, significant specimen-specific variation was observed. Worrisome declines were noted for piperacillin-tazobactam in bloodstream infections (81.8–64.7%, p

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