Direct identification of microorganisms from positive blood cultures by MALDI-TOF MS using an in-house saponin method

- Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a fast and reliable method for the identification of bacteria.
- Pretreatment is necessary to prepare samples obtained directly from culture bottles.
- Three pretreatment methods, including an in-house saponin method, were compared.
- The saponin method was not inferior in accuracy as compared to the commercial kit.
- The lower cost of the saponin method will contribute to identifying blood-borne pathogens.

SummaryObjectivesMatrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a fast and reliable method for the identification of bacteria. A MALDI Sepsityper kit is generally used to prepare samples obtained directly from culture bottles. However, the relatively high cost of this kit is a major obstacle to introducing this method into routine clinical use. In this study, the accuracies of three different preparation methods for rapid direct identification of bacteria from positive blood culture bottles by MALDI-TOF MS analysis were compared.MethodsIn total, 195 positive bottles were included in this study.ResultsOverall, 78.5%, 68.7%, and 76.4% of bacteria were correctly identified to the genus level (score ≥1.7) directly from positive blood cultures using the Sepsityper, centrifugation, and saponin methods, respectively. The identification rates using the Sepsityper and saponin methods were significantly higher than that using the centrifugation method (Sepsityper vs. centrifugation, p < 0.001; saponin vs. centrifugation, p = 0.003).ConclusionsThese results suggest that the saponin method is superior to the centrifugation method and comparable to the Sepsityper method in the accuracy of rapid bacterial identification directly from blood culture bottles, and could be a less expensive alternative to the Sepsityper method.