Comparison of two methods skipping cell lysis and protein extraction for identification of bacteria from blood cultures by matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry.

OBJECTIVE: Matrix-assisted laser desorption/ionization time-of-flight mass-spectrometry (MALDI-TOF MS) is widely used for fast identification of bacteria from blood cultures (BC). We compared the performance of two procedures, one including a pre-enrichment step in brain heart infusion and the other a direct method using vacutainer separator gel tubes (DI), for identification of bacteria from blood cultures by MALDI-TOF MS. METHODS: We first prepared a training set of 20 simulated bacteremia specimens, including 10 Gram-negative and 10 Gram-positive species. A total of 145 non-consecutive BCs flagged as positive (68 Gram-negative rods, and 77 Gram-positive cocci) were prospectively analyzed (validation set). RESULTS: A total of 82% and 49% of isolates were correctly identified to the species level by the respective methods. CONCLUSIONS: The pre-enrichment method outperformed the DI method for identification of virtually all bacterial species included in the panels.