Comparison of European Committee on Antimicrobial Susceptibility Testing (EUCAST) and CLSI screening parameters for the detection of extended-spectrum β-lactamase production in clinical Enterobacteriaceae isolates.

OBJECTIVES: To compare the performance of European Committee on Antimicrobial Susceptibility Testing (EUCAST) and CLSI breakpoints following their revision in 2010, for the detection of extended-spectrum β-lactamase (ESBL) production in Enterobacteriaceae.

METHODS: 236 well-characterized clinical isolates (including 118 ESBL producers) were investigated by antibiotic disc testing with cefpodoxime, ceftriaxone, cefepime, cefotaxime EUCAST (5 μg/disc), ceftazidime EUCAST (10 μg/disc), cefotaxime CLSI (30 μg/disc) and ceftazidime CLSI (30 μg/disc) with the Kirby-Bauer method. Additionally, synergy phenomena were recorded between amoxicillin/clavulanic acid discs (20/10 μg/disc) and cefepime (30 μg/disc), EUCAST cefotaxime (5 μg/disc), EUCAST ceftazidime (10 μg/disc), CLSI cefotaxime (30 μg/disc) and CLSI ceftazidime [30 μg/disc; disc approximation method (DAM)].

RESULTS: Overall sensitivity of the cefotaxime EUCAST non-susceptible breakpoint equalled sensitivity of the cefotaxime CLSI ESBL screening breakpoint (99.2%). With the ceftazidime EUCAST non-susceptible breakpoint, 27/118 ESBL-producing isolates were not detected, whereas the ceftazidime CLSI ESBL screening breakpoint missed 41/118 ESBL-producing isolates. For cefpodoxime the resistant EUCAST breakpoint showed higher sensitivity for ESBL detection compared with the CLSI ESBL screening breakpoint/disc content (100% versus 98.3%, respectively). Sensitivities of ceftazidime and cefotaxime DAM with CLSI or EUCAST disc contents were comparable (sensitivities ranging from 84.7% to 89.8%). DAM with cefepime displayed the highest overall sensitivity (96.6%). In AmpC-producing isolates, synergy of amoxicillin/clavulanic acid with cefepime showed sensitivity and specificity for ESBL detection of 100% and 97.4%, respectively.

CONCLUSIONS: EUCAST non-susceptible breakpoints for ceftazidime and cefpodoxime detect more ESBL-producing Enterobacteriaceae isolates compared with corresponding CLSI ESBL screening breakpoints. Implementation of the cefepime DAM can facilitate ESBL screening, especially in strains producing an AmpC β-lactamase since the test shows high sensitivity and specificity.