Purpose: The MS was validated according to AOAC guidelines for Performance Tested Methods and Official Methods precollaborative studies for the identification of microorganisms.
Methods: In the combined internal and independent laboratory studies 359 different claimed organisms (representing 208 Gram negative, 123 Gram positive and 28 yeast) were evaluated by the method. All test strains were cultured on appropriate agar medium and growth conditions before analyzing on the MS instrument.
Results: Overall percent correct identification in the combined Internal and Independent studies (6111/6401 MS results from the 359 different organisms) was 95.5%. For each specific group of microorganisms tested the percent correct identification was 94.4% for Gram-negative organisms, 96.1% for Gram-positive organisms and 97.5% for yeast. Assay ruggedness was demonstrated for three critical parameters, including the use of 1-µl loops from two different suppliers, the age of the culture on an agar plate before analysis and various suppliers of the agar media.
Significance: Overall results indicate that the VITEK MS method is an acceptable automated method for the identification of a wide variety of yeasts, Gram-negative and Gram-positive bacteria.