Phenotypic Detection of Plasmid-Mediated Colistin Resistance in Enterobacteriaceae

The aim of this work was to evaluate an easy-to-perform assay based upon inhibition of mobile colistin resistance (MCR) activity by EDTA. We included 92 nonrelated isolates of Enterobacteriaceae (74 Escherichia coli , 17 Klebsiella pneumoniae , and 1 Serratia marcescens ). Our proposed method is based on a modification of the colistin agar-spot screening test (CAST), a plate containing 3 μg/ml colistin, by adding an extra plate of colistin agar-spot supplemented with EDTA (eCAST).