Phenotypic testing for Enterobacterales that harbour ESBLs is not additive to accurate in vitro β-lactam MICs for clinical decision-making. ESBL testing is an outdated practice established in an era of higher cephalosporin breakpoints to prevent resistant Enterobacterales carrying Ambler class A β-lactamases with affinity for later-generation β-lactams from being reported as susceptible to later-generation cephalosporins, leading to clinical failures. ESBL testing is problematic because of inaccuracies when multiple classes of β-lactamases are produced by the same organism, thus limiting the testing application to specific species and resistance types. Clinical laboratories should instead focus finite resources on accurate susceptibility testing using contemporary interpretative criteria to help guide therapeutic decisions. With continued emergence of antimicrobial resistance and in the setting of accurate susceptibility testing and current breakpoints the use of ESBL phenotypic testing is not helpful in clinical decision-making.
© The Author(s) 2021. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy.