Evaluation of the Reliability of Automated Colistin Susceptibility Assays of Pseudomonas aeruginosa

Abstract

Background: With the increase in multidrug-resistant (MDR) gram-negative rods, colistin treatment is increasingly required. Reliable susceptibility testing is important for managing infectious patients with MDR Pseudomonas aeruginosa . This study evaluated the reliability of an automated colistin susceptibility assay. Methods: In total, 195 non-duplicated P. aeruginosa blood isolates were collected from nine sentinel hospitals in Korea in 2020. Colistin susceptibility with Sensititre KNIHCOL Trek diagnostic system (Thermo Fisher Scientific, England), a commercial broth microdilution (BMD), was compared with that of the gram-negative MIC panel type 44 card (Beckman Coulter, USA). Isolates with discrepant results were reconfirmed using AST-N225 (bioMérieux SA, France). Results: Categorical agreement was 92.8%, and nine colistin-resistant isolates with BMD were colistin-intermediate with two automated colistin susceptibility assays. Conclusions: The failure to detect colistin-resistant P. aeruginosa could not be safely excluded with an automated colistin susceptibility assay.