Bacterial rapid identification with matrix assisted laser desorption/ionization time-of-flight mass spectrometry: development of an 'in-house method' and comparison with Bruker Sepsityper® kit

Objective: The objective of this study was to compare an in-house matrix-assisted laser desorption ionization with time of flight (MALDI-TOF) method and a commercial MALDI-TOF kit (Sepsityper (R) kit) for direct bacterial identification in positive blood cultures. We also evaluated the time saved and the cost associated with the rapid identification techniques. Methods: We used the BACTEC (R) automated system for detecting positive blood cultures. Direct identification using Sepsityper kit and the in-house method were compared with conventional identification by MALDI-TOF using pure bacterial culture on the solid phase. We also evaluated different cut-off scores for rapid bacterial identification. Results: In total, 127 positive blood vials were selected. The rate of rapid identification with the MALDI Sepsityper kit was 25.2% with the standard cut-off and 33.9% with the enlarged cut-off, while the results for the in-house method were 44.1 and 61.4%, respectively. Error rates with the enlarged cut-off were 6.98 (n=3) and 2.56% (n=2) for Sepsityper and the in-house method, respectively. Identification rates were higher for gram-negative bacteria. Discussion: Direct bacterial identification succeeded in supplying rapid identification of the causative organism in cases of sepsis. The time taken to obtain a result was nearly 24 hours shorter for the direct bacterial identification methods than for conventional MALDI-TOF on solid phase culture. Compared with the Sepsityper kit, the in-house method offered better results and fewer errors, was more cost-effective and easier to use.