Two-year antimicrobial susceptibility trends of Escherichia coli in a tertiary care centre: A retrospective analysis
Abstract
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 notedforpiperacillin-tazobactaminbloodstreaminfections(81.8–64.7%, p<0.05)andforciprofloxaciningynaecologicalsamples(41.4–23.0%). Encouragingly, pus isolates showed marked improvement across multiple antibiotic classes, with increases exceeding 15% for several agents. Conclusions: Our findings highlight both the strengths and weaknessesof our current antibioticarsenal. Whilecarbapenems and urinary agentsremain effective, the declining reliability of piperacillin-tazobactam and ciprofloxacin in specific infection types demands attention. The marked variation by specimen type reinforces the need for site-specific empirical guidelines rather than one-size-fits-all protocols. Regular local surveillance and robust antimicrobial stewardship are essential to preserve the effectiveness of our remaining reliable antibiotics.