LABORATORY DETECTION OF COLISTIN-RESISTANT <i>ENTEROBACTERALES</i> IN TANDEM WITH ROUTINE ANTIBIOGRAM

Since the emergence and spread of carbapenemase-producing Enterobacterales, particularly those carrying metallo-β-lactamases with 16S rRNA methyltransferases for which newly introduced antibiotics are inactive, colistin is a last resort therapy for life-threatening extensively drug-resistant infections. This requires that laboratories use an accurate and reliable method for routine colistin susceptibility testing. The aim of this study was to evaluate the performance and applicability of a colistin screening medium for detection of colistin-resistant isolates simultaneously with routine susceptibility testing. It was evaluated with fifty colistin-resistant and the same number of colistin-susceptible comparator isolates. Our results showed that all colistin-resistant isolates grew on DiaPlate™ EMB Agar + Colistin medium within the standard antibiogram period. In contrast, no growth was observed among the colistin susceptible comparators. DiaPlate™ EMB Agar + Colistin is a screening medium that can detect colistin- resistant Enterobacterales isolates when pure bacterial cultures are tested. As this method for detecting colistin-resistant isolates uses the same inoculum as the Kirby-Bauer method, the screening test for colistin resistance can be conveniently performed on clinical isolates along with routine antimicrobial susceptibility testing.