Impact of CLSI and EUCAST Cefepime breakpoint changes on the susceptibility reporting for Enterobacteriaceae.

OBJECTIVE

We analyzed the effects of different cefepime MIC breakpoints on Enterobacteriaceae cefepime susceptibility and the presence of AmpC and extended-spectrum β-lactamase (ESBL) genes within the cefepime MIC interpretative categories.

METHODS

Using Enterobacteriaceae susceptibility data from 2013 comparisons of MIC breakpoints were performed using Pearson's chi-squared test. Molecular testing on a subset of isolates was done.

RESULTS

Among 3784 non-duplicate clinical isolates, cefepime susceptibility decreased from 97.6% to 96.1% to 93.7% for CLSI 2013, CLSI 2014, and EUCAST 2011, respectively. In ceftriaxone non-susceptible isolates, cefepime susceptibility decreased from 79% to 66% (P<0.0001) using CLSI 2013 and 2014, respectively, which was greater and statistically significant for Escherichia coli and Klebsiella spp. but not for Enterobacter spp. (P=0.06). Isolates with MIC ≤1μg/mL more often harbored AmpC (77%) than ESBL (18%) genes.

CONCLUSIONS

Lower cefepime MIC breakpoints decrease cefepime susceptibility for isolates harboring ESBLs, while sparing the majority of those with AmpCs.