Laboratory evaluation of Brilliance™ CRE Agar for screening carbapenem-resistant Enterobacteriaceae: Performance on a collection of characterised clinical isolates from Greece

Abstract

The performance of Oxoid Brilliance™ CRE Agar (BCRE), a new chromogenic medium designed for screening of carbapenem-resistant Enterobacteriaceae, was evaluated on a collection of clinical isolates of enterobacteria (n=175) and non-fermenters (n=55) with known β-lactam resistance mechanisms and levels of susceptibility to carbapenems. BCRE supported the growth of 100 of 108 enterobacterial isolates that were non-susceptible to at least one carbapenem, whilst excluding 57 of the 67 carbapenem-susceptible isolates. The eight non-susceptible isolates that did not grow on BCRE were carbapenemase-producers with low carbapenem minimum inhibitory concentrations, mostly exhibiting non-susceptibility only to one carbapenem. In total, of 107 carbapenemase-producing enterobacteria that were included in the study, 16 did not grow, with most of them being either susceptible (n=8) or intermediate-susceptible (n=5) to carbapenems. Regarding the 10 carbapenem-susceptible enterobacteria that were not excluded by BCRE, 1 produced a carbapenemase and the rest possessed strong backgrounds of various other β-lactam resistance mechanisms. The medium allowed growth of almost all carbapenem-resistant non-fermenting isolates; nevertheless, non-fermenters were clearly differentiated from Enterobacteriaceae by colony colour and morphology.

Keywords: Brilliance™ CRE Agar; Carbapenemase detection; Carbapenemase-producing Enterobacteriaceae; Chromogenic culture media; Screening cultures.