Evaluation of an optimized method to directly identify bacteria from positive blood cultures using MALDI-TOF mass...

Although various methods have been developed to directly identify bacteria from positive blood cultures by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS), the necessity of using commercial kits still leads to a high cost and long assay time. Moreover, few evaluations of these methods have been conducted. This study aimed to evaluate the feasibility of an optimized MALDI-TOF MS method for direct identification of bacteria in positive blood cultures.

A total of 829 non-repeated positive cultures were collected from July 2018 to August 2019, and direct identification was performed by an optimized MALDI-TOF MS method. The same positive blood cultures were sub-cultivated to obtain a single bacterial colony and identified by classical biochemical BD testing, which is the gold standard to compare the accuracy of direct identification of positive blood cultures by MALDI-TOF MS.

After excluding 7 false-positive samples from the 829 positive blood cultures, the most accurate rate of direct identification by this optimized MALDI-TOF MS method was for gram-negative bacteria (91.5%), followed by gram-positive bacteria (88.3%), fungi (84.8%), anaerobic bacteria (80%), and other rare bacteria (66.67%).

Common bacteria in positive blood cultures can be identified directly within 1 hour by MALDI-TOF MS, and thus, this optimized method can be used as a primary identification method by clinicians. Routine implementation of this method may significantly increase the optimal utilization rate of antibiotics and decrease mortality in bacteremia patients.