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Improving diagnostics in the fungal field

Differentiation at species level of the members of the PSC complex (Pseudallescheria boydii/Scedosporium apiospermum) involved in cystic fibrosis by MALDI-TOF MS (VITEK MS®)

April 21 • O1260

V. Monnin1, L. Picoulet1, D. Giraud1, S. Arend1, B. Celliere1, P. Courault2, D. Pincus3, G. Durand1, V. Girard1

1) R&D Microbiology, bioMérieux, La Balme-les-Grottes, France
2) R&D biomathématiques, bioMérieux, La Balme-les-Grottes, France
3) R&D Microbiology, bioMérieux, Inc., Hazelwood (MO), USA

Background: The species of the Pseudallescheria boydii/Scedosporium apiospermum complex (PSC) are ubiquitous molds reported as emerging pathogens causing invasive fungal diseases and colonization especially in cystic fibrosis (CF) patients, with a prevalence of about 10%. The distinction of the species within the complex is of great importance as they show different antifungal susceptibility profiles to azoles or echinocandins.
The current molecular methods can be fastidious and time-consuming. In this study, we propose a rapid identification of these organisms at species level via an inactivation/extraction protocol followed by a MALDI-TOF MS identification.

Materials/methods: A total of 343 spectra from 64 well-characterized PSC strains (Pseudallescheria boydii (n=5), Pseudallescheria ellipsoidea (n=4), Pseudallescheria minutispora (n=4), Scedosporium apiospermum (n=17), Scedosporium aurantiacum (n=4), Scedosporium dehoogii (n=4),and Scedosporium prolificans (n=6)) were acquired with the VITEK® MS after an inactivation/extraction protocol and within the mass range of 3000-17000 Da.
The spectra were integrated into the next VITEK® MS knowledge base update and data were analyzed using dendrograms and multidimensional scaling (MDS). Performance was evaluated using a cross-validation approach.

Results: The MDS shows that a clear differentiation is possible between all species of the complex despite a very high spectrum similarity (>50%) as shown by the dendrogram analysis.
The cross validation study performed on the updated database, containing 15557 spectra covering 327 fungal species, shows that 97.7 to 100% correct identification rates are obtained at the species level for all seven species.

Conclusions: This study demonstrates that MALDI-TOF MS is a rapid and reliable tool to differentiate close species within the PSC complex. It could help in the management of CF patients by improving the identification of molds responsible for colonization and by reducing the time to start appropriate antifungal therapy.



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