Purpose Colistin represents one of the last treatment options for infections caused by multi-drug resistant (MDR) Enterobacterales . The emergence of a plasmid-mediated mobile colistin resistance-1 ( mcr-1 ) gene has raised serious concerns about its potential dissemination among bacteria. Methods In this study, we evaluated the chromogenic medium, CHROMID ® Colistin Resistance (COLR) agar, for the rapid detection of colistin-resistant Enterobacterales using broth microdilution (BMD) as a reference method. We also attempted to detect mcr-1 , −2 , −3 , −4 , and −5 genes, as well as the insertion sequence IS Apl1 via polymerase chain reaction (PCR), followed by sequencing of mcr gene(s). Results Among the 100 studied Enterobacterales isolates, 53% of them were colistin-resistant, with higher rate among Klebsiella pneumoniae (75%) as compared to Escherichia coli (44.4%). The COLR agar showed 83.2% sensitivity and 97.9% specificity for the detection of colistin resistance. Among colistin-resistant isolates, mcr-1 gene was only detected in four (7.5%) E. coli isolates. The IS Apl1 was not found among mcr-1 positive isolates. Sequencing of mcr-1 gene revealed nucleotide sequence homogeneity with the wild-type mcr-1 gene in BLAST. Conclusion The COLR agar is a promising phenotypic method for the detection of colistin-resistant Enterobacterales . Multiplex PCR followed by sequencing can be used for mcr genes’ detection and characterization.

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