Impact of direct identification of bacteria in blood culture–positive specimens by matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry on physician selection of antimicrobial therapy

Background: Rapid identification of the causative organism in blood stream infections is essential for early initiation of appropriate antimicrobial therapy. Direct identification of bacteria in positive blood culture bottles using matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry is a promising application. A variety of direct identification methods have been reported; however, few studies have evaluated the impact of these methods on physician decision making regarding antimicrobial therapy. Methods: We developed a simple method for direct bacterial identification and applied it to daily clinical practice to investigate the impact of direct identification of bacteria in positive blood culture bottles on physicians’ choice of antimicrobial agents for treatment. Results: From January 2016 to December 2022, we attempted direct identification in 98 cases and successfully acquired identification results in 88 cases. In three cases, no empiric antimicrobial agents were initiated at the time of venipuncture for blood culture but later initiated based on the direct identification results. In the remaining 85 cases, empiric antimicrobial therapy was initiated at the time blood cultures were performed, and in 29 cases, empiric antimicrobial therapy was changed after direct identification. In 17 of these 29 cases, the antimicrobial therapy was changed based on the direct identification of bacterial genus/species, resulting in a change to an effective antimicrobial therapy before the antimicrobial susceptibility testing results were available. Conclusions: Direct identification of bacteria from positive blood culture bottles could contribute to earlier selection of or changes to antimicrobial therapies by attending physicians.