A Resazurin Reduction-Based Assay for Rapid Detection of Polymyxin Resistance in Acinetobacter baumannii and Pseudomonas aeruginosa.

ABSTRACT

A rapid test was developed for identification of polymyxin resistance in nonfermenting bacteria. This test detects viable cells after growth in a medium containing a defined concentration of colistin. The principle of this test is based on the visual detection of the reduction of the resazurin reagent, a viability colorant, as observed by its color change (blue to purple or pink). Its evaluation was performed by using 92 colistin-resistant and colistin-susceptible Acinetobacter baumannii and Pseudomonas aeruginosa isolates. Sensitivity and specificity were found to be 100% and 95%, respectively, by comparison with the standard broth microdilution method. The Rapid ResaPolymyxin Acinetobacter/Pseudomonas NP test is inexpensive, easy to perform, highly sensitive and specific, and can be completed in 4 hours. It could be useful in countries facing endemic spread of colistin-resistant nonfermenters.