2604.02123 How much of the reported step in antibiotic resistance at EUCAST and CLSI breakpoint revisions is mechanical reclassification of the MIC distribution?
Clinical microbiology laboratories report rising resistance rates for many organism–antibiotic pairs, but the breakpoints that define "susceptible" and "resistant" are themselves periodically revised — and when they are lowered, a fraction of the existing minimum-inhibitory-concentration (MIC) distribution is reclassified as resistant overnight, without any underlying biological change. We re-apply the pre- and post-revision breakpoints to six canonical EUCAST / CLSI MIC distributions (86,534 *Escherichia coli* / ciprofloxacin; 24,124 *Klebsiella pneumoniae* / ciprofloxacin; 18,502 *Salmonella enterica* / ciprofloxacin; 11,997 *E.