Evaluation of species-specific score cut-off values for various Staphylococcus species using a MALDI Biotyper-based identification

Although previous studies investigating the MALDI Biotyper database (matrix-assisted laser desorption/ionization time-of-flight mass spectrometry-based identification) have proven its high accuracy for bacterial identification, the studies differed in sample preparation, number of replicates, quantity of shots and target types used. In particular, the score cut-off values of special importance for reliable species identification varied. The aim of the present study was to identify species-specific differences in the mean score values for staphylococci. Cut-off values recommended by the manufacturer were adapted using the 20th percentile to rule out unknown score-modifying factors, even though the specificity was high and the lowest cut-off values would also yield an accurate result. Whilst correct species diagnosis was obtained in 97.32% of samples (1382/1420), only 220 of all duplicates (15.49%) revealed a score of >= 2.3, whilst 968 (68.17%) had a score between 2.0 and 2.299, and 194 (13.66 %) had a score of <2.0. Ten of 21 species had a calculated 20th percentile of <2.0 and one species of <1.7. In conclusion, the use of species-specific cut-off values improves the relative sensitivity of species identification in staphylococci.