Rapid Polymyxin/Pseudomonas NP test for rapid detection of polymyxin susceptibility/resistance in Pseudomonas aeruginosa.

Polymyxins are becoming an added value for treating infections due to multidrug-resistant Pseudomonas aeruginosa. Therefore, the Rapid Polymyxin/Pseudomonas NP test was developed for the identification of polymyxin resistance in P. aeruginosa isolates. This test detects the bacterial growth in a medium containing a defined concentration of colistin. Formation of basic metabolites is visually detected by yellow to purple/violet color change of the bromocresol purple pH indicator. The test performance was evaluated by using 50 colistin-resistant and colistin-susceptible P. aeruginosa isolates, among which 10 were colistin resistant. The sensitivity and specificity of the test were found to be 100% (CI95 65.5-100%) and 95% (CI95 81.8-99.1%), respectively, by comparison with broth microdilution as the reference method. The Rapid Polymyxin/Pseudomonas NP test is easy to perform, specific and sensitive, allowing rapid visual observation of results without the requirement any special reading equipment, and results are obtained in 3 h.