Use of WalkAway MicroScan system colistin well when determining the susceptibility of Pseudomonas aeruginosa and Acinetobacter baumannii recent clinical isolates.

Abstract

The increasing prevalence of multidrug-resistant non-fermenting Gram-negative bacilli has led to a resurgence in the use of colistin for treating infections caused by these microorganisms. However, assessing colistin susceptibility remains challenging in microbiology laboratories. Common methods, such as disc diffusion and E-test, have been deemed unreliable due to high rates of false resistance. According to EUCAST guidelines, the gold standard for colistin susceptibility testing is broth microdilution, despite its labor-intensive manual process. Automated alternatives, such as Sensititre (ThermoFisher Diagnostics) and MicroScan (Beckman Coulter), have shown false resistance rates of up to 65%. A promising method aligned with EUCAST recommendations is the manual microdilution used in the UMic test (BioCentric), which our laboratory employs to confirm resistance results obtained from the MicroScan system. This study aims to compare the performance of automated MicroScan and E-test (gradient diffusion) methods against the manual UMic microdilution method.