A vancomycin-resistant Enterococcus faecium isolate from a Danish healthy volunteer, detected 7 years after the ban of avoparcin, is possibly related to pig isolates

547 previously with the VITEK2 system and (as here) with the cefotaxime ESBL Etest.5,6 Cefpodoxime–clavulanate combination disc tests were reliable in distinguishing ESBL producers from hyperproducers of K1 enzyme, but are unlikely to be ideal for AmpC-inducible organisms, e.g. Enterobacter spp. Herein is the key point: as ESBLs become more complex, diverse and widespread, the likelihood of any single test being universally appropriate for their detection must diminish. Rather than depending solely on such tests, the best chance of accurate ESBL detection lies in considering the overall MIC profile together with the results of any ‘specific’ ESBL test. Hyperproducers of K1 β-lactamase are not difficult to distinguish from ESBL producers, being consistently resistant to cefuroxime, piperacillin–tazobactam and aztreonam, having borderline resistance to cefotaxime and cefepime, but remaining fully susceptible to ceftazidime. This is not the typical pattern for any ESBL. Hyperproducers of K1 enzyme are only likely to be mistaken for ESBL producers if ‘ESBL tests’ are naively taken as the sole criterion for defining ESBL production, or if inadequately narrow batteries of antibiotics are tested.