In-house rapid colorimetric method for detection of colistin resistance in Enterobacterales: A significant impact on resistance rates.

A rapid colorimetric method, the Andrade Screening Antimicrobial Test (ASAT) was evaluated to detect colistin resistance in Enterobacteriales clinical isolates. The sensitivity and specificity were 90.7% and 100%, respectively. In 10/26 E. coli isolates the automatized method failed to detect the resistance, whereas the ASAT detected it accurately. Most of these isolates showed COL MIC values in the range 4-8 µg mL-1 and carried mcr-1. As regards K. pneumoniae COL- resistant isolates, discrepancies between the Phoenix system and the ASAT were observed only in 3/44 isolates, most of them carried the blaKPC gene and showed COL MIC values >16 µg mL-1.