Direct identification of bacteria from charcoal-containing blood culture bottles using matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry

Several protocols for direct matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF MS) from positive blood cultures are currently used to speed up the diagnostic process of bacteraemia. Identification rates are high and results are accurate for the BACTEC? system and for charcoal-free bottles. Only a few studies have evaluated protocols for charcoal-containing BacT/ALERT bottles reaching substantially lower identification rates. We established a new protocol for sample preparation from aerobic and anaerobic positive charcoal-containing BacT/ALERT blood culture bottles and measured the protein profiles (n?=?167). Then, we integrated this protocol in the routine workflow of our laboratory (n?=?212). During the establishment of our protocol, 74.3?% of bacteria were correctly identified to the species level, in 23.4?%, no result and in 2.4?%, a false identification were obtained. Reliable criteria for correct species identification were a score value?≥1.400 and a best match on rank 1-3 of the same species. Identification rates during routine workflow were 77.8?% for correct identification, 20.8?% for not identified samples and 1.4?% for discordant identification. In conclusion, our results indicate that MALDI-TOF MS is possible, even from charcoal-containing blood cultures. Reliable criteria for correct species identification are a score value?≥1.400 and a best match on rank 1-3 of a single species.