Evaluation of Influence Factors in the Identification of Clinical Filamentous Fungi by Matrix Assisted Laser Desorption Ionization-time of Flight Mass Spectrometry

  Objective  This study aimed to evaluate the potential influence of culture conditions, incubation time, and the interpreting cut-off value(COV) in the identification of filamentous fungi by matrix-assisted laser desorption ionization-time of flight mass spectrometry(MALDI-TOF MS).

  Methods  Seventy-eight isolates of filamentous fungi were cultivated in sabouraud dextrose agar(SDA) or potato dextrose agar(PDA) media with an incubation temperature of 28℃ or 35℃ separately, namely four different culture conditions.MALDI-TOF MS identification was carried out at different time including the 2nd, 3rd, 4th, 5th and 7th days of incubation of the isolates. Differences in identification capacities of MALDI-TOF MS under the tested parameters were analyzed to determine the optimal culture condition and incubation time of filamentous fungi. The influence of lowered interpreting COV in MALDI-TOF MS identification of filamentous fungi was also evaluated.

  Results  No significant difference was detected between the SDA and PDA culture media in the identification capacities of MALDI-TOF MS(χ²=0.467, P=0.792). The identification capacity of MALDI-TOF MS with the incubation temperature of 28℃ was superior to that of 35℃(χ²=7.195, P=0.027). Higher identification rates of species level(40.3%, 34.3%) and genus level(44.8%, 46.3%) were achieved in isolates incubated for 2 and 3 days. The identification rate of species level was increased significantly from 32.1% to 85.9%(χ²=40.119, P < 0.01) without increasing the false identification rate after adjusting the interpreting COV from score > 2.0 to > 1.7.

  Conclusion  The performance of MALDI-TOF MS in the identification of filamentous fungi could be improved by applying the optimal culture condition of incubating in SDA or PDA media under the temperature of 28℃ for 2 to 3 days and by adjusting the interpreting COV of the species level with a score > 1.7.