Evaluation of blood culture broths with lysis buffer to directly identify specific pathogens by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry methods Maya Hariu,1,2 Yuji Watanabe,1,2 Nozomi Oikawa,1,2 Takafumi Manaka,1,2 Masafumi Seki1 1Division of Infectious Diseases and Infection Control, Tohoku Medical and Pharmaceutical University Hospital, Sendai City, Miyagi, Japan; 2Department of Laboratory Medicine, Laboratory for Clinical Microbiology, Tohoku Medical and Pharmaceutical University Hospital, Sendai City, Miyagi, Japan Background: Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is now widely used to detect pathogens in clinical settings in Japan. Method: Here, we report the effects of adding lysis buffer in the MALDI-TOF MS method to directly detect bacteria from 3 blood culture systems and compare their detection efficiencies for each pathogen. Results: Blood culture broths from BD, bioMérieux, and Oxoid showed similar detection efficiencies without lysis buffer use and Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa were efficiently detected in all broths when lysis buffer was used. However, Streptococcus pneumoniae was not detected in BD broth when lysis buffer was added. Furthermore, Haemophilus influenzae and Bacteroides fragilis were not detected in all 3 systems when lysis buffer was used. Conclusion: Optimization of blood culture system and lysis buffer is necessary according to each pathogen for direct identification by MALDI-TOF MS methods. Keywords: blood cultures broth, lysis buffer, Escherichia coli, Haemophilus influenzae, Streptococcus pneumoniae, time-of-flight mass spectrometry