EDTA-cefoxitin-agar medium for laboratory detection of AmpCβ-lactamases in Enterobacteriaceae and its preliminary clinical application

Objective To set up and evaluate a new ethylenediamine tetra-acetic acid(EDTA)-cefoxitin(FOX)- agar medium(E-CAM)for detecting ampicillin cephamycinβ-lactamases(AmpC)in Enterobacteriaceae.Methods The E-CAM method was compared to the previously published three-dimensional extract method(TDEM)for the detec- tion of AmpC.Clinical isolates of FOX-resistant Enterobacteriaceae were tested by both methods.Positive control(Enter- obacter cloacae 029M)and negative control(Escherichia coli ATCC 25922)strains were included on each plate.Re- sults The E-CAM method with 6μg/mL of FOX and 750μg of EDTA were similar to the TDEM method for detecting AmpC production in Enterobacteriaceae,the coincidence rate was 100%.Conclusions The new method is easier to perform and interpret and allows for testing multiple isolates on a single plate.Clinical laboratories can use this tech- nique to detect the presence of AmpC enzyme.