Direct fast identification of bacteria in positive blood culture presents key information for laboratory personel as well as for the coresponding clinician. Polymicrobial bacteremia correlate with a higher death risk and present a longer period of recovery than do monomicrobial bacteremias. Using the module Sepsityper we wanted to obtain information about the possible presence of more than one microorganism in blood culture. We thus wanted to evaluate the analysis of mass spectra of positive blood cultures with the standard MALDI Biotyper Compass and compare it to the analysis of mass spectra obtained via module Sepsityper for identification of mixed cultures. Our gold standard was the coresponding culture of hemoculture on agar plates. We also wished to determine the optimal ratio between two bacterial species for which the Sepsityper module would still give us a sufficient result. We concluded that the Sepsityper module isn't appropriate for the characterization of polymicrobial spectra. Through the Sepsityper settings we identified only 4 out of 46/58 polymicrobial blood cultures for which it determined some spectra, i.e. got a response. In our experiment, the optimal ratio for differentiating between two bacterial species was 1:1, with the lowest being 8:1 and at a ratio of 20:1 Sepsityper module could not differentiate the two any longer.
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