Comparative analysis of disk diffusion and microscan versus broth microdilution methods for determining antimicrobial susceptibility of cefepime and piperacillin-tazobactam in Escherichia coli isolates c

Routine susceptibility testing often misses resistance in bla _OXA-1 -producing E. coli , risking therapeutic failure. Among 165 clinical isolates from the Spanish multicenter cohort, MicroScan and disk diffusion versus reference broth microdilution yielded suboptimal categorical agreement (73.9%–86.7%) for piperacillin-tazobactam (PTZ) and cefepime (FEP). MicroScan PTZ very major errors (30%) indicate resistance underestimation; disk diffusion PTZ major errors (23%) and both methods FEP major errors (8.3%–13.8%) indicate resistance overestimation. These errors justify cautious interpretation of routine susceptibility results.