Does the presence of multiple β-lactamases in Gram-negative bacilli impact the results of antimicrobial susceptibility tests and extended-spectrum β-lactamase and carbapenemase confirmation methods?

•Disk diffusion testing remains accurate even in the presence of multiple β-lactamases.•mCIM/eCIM and Xpert Carba-R accurately differentiate between serine and metallo-β-lactamases.•ESBL screening tests produced inconsistent results that may confound therapy.•Predicting carbapenem resistance from WGS data produces very major errors.