Optimal turnaround time for direct identification of microorganisms by mass spectrometry in blood culture

• Identification of microorganisms directly performed from positive blood culture.
• A short hands-on time and a turnaround time shorter than 15 min
• 77.8% of detection at the species level with positive predictive value of 99.5%
• The method can easily take place in the workflow of a laboratory with low staff.

IntroductionDuring the past few years, several studies describing direct identification of bacteria from blood culture using mass spectrometry have been published.These methods cannot, however, be easily integrated into a common laboratory workflow because of the high hands-on time they require. In this paper, we propose a new method of identification with a short hands-on time and a turnaround time shorter than 15 min.Materials and methodsPositive blood bottles were homogenised and 600 μL of blood were transferred to an Eppendorf tube where 600 μL of lysis buffer were added. After homogenisation, a centrifugation step of 4 min at 10,500g was performed and the supernatant was discarded. The pellet was then washed and loaded in quadruplicate into wells of a Vitek® MS-DS plate. Each well was covered with a saturated matrix solution and a MALDI-TOF mass spectrometry analysis was performed. Species were identified using the software Myla 3.2.0-2.ResultsWe analysed 266 positive blood culture bottles. A microorganism grew in 261 cultures, while five bottles remained sterile after 48 h of incubation in subculture. Our method reaches a probability of detection at the species level of 77.8% (203/261) with a positive predictive value of 99.5% (202/203).ConclusionWe developed a new method for the identification of microorganisms using mass spectrometry, directly performed from a positive blood culture. This method has short hands-on time and turnaround time and can easily take place in the workflow of a laboratory, with comparable results in performance with other methods reported in the literature.