Detection of plasmid-mediated colistin resistance by colistin pre-diffusion and inhibition with EDTA test (CPD-E) in Enterobactereaceae.

A phenotypic assay based on colistin pre-diffusion and differential inhibition of Mobile Colistin Resistance (MCR) protein activity by EDTA showed that, of the 92 strains tested, all MCR producers (49) exhibited an increase ≥5 mm in the inhibition zone around the area of pre-diffusion in the presence of EDTA, in comparison with colistin alone. Results suggest that CPD-E may differentiate MCR-producing microorganisms from resistant microorganisms without this marker.