RapidResa Polymyxin NP Test for Rapid Detection of Polymyxin Resistance in .

A homemade and culture-based test, relying on the visual detection of the reduction of the resazurin reagent (a cell viability indicator), has been developed for the rapid detection of polymyxin resistance in . Here, we evaluated the industrial version of this test, the RapidResa Polymyxin NP test (Liofilchem, Italy). A well-characterized panel of 68 clinical strains (36 polymyxin-susceptible, 26 polymyxin-resistant , and 6 colistin-heteroresistant isolates) of worldwide origin was tested. All the colistin-susceptible isolates gave negative results according to the RapidResa Polymyxin NP test, except for a single isolate that gave a false-positive result. Out of the 26 colistin-resistant strains, 25 were correctly identified as colistin resistant using the RapidResa Polymyxin NP test. Only a single colistin-resistant strain gave a false-negative result. Additionally, the six colistin-heteroresistant isolates tested gave positive results. Altogether, the sensitivity and the specificity of the test were found to be 96% and 97%, respectively. The turn-around-time of this easy-to-perform test was 3-4h, which showed excellent reliability for identification of polymyxin resistance in . The RapidResa Polymyxin NP test allows a rapid differentiation between polymyxin-susceptible and -resistant isolates, which may contribute to optimization of the use of polymyxins for treating infections due to multidrug-resistant