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Improvement of maldi-tof for the identification of Aeromonas salmonicida and Aeromonas bestiarum : two important fish pathogen
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International audience. The identification of Aeromonas isolates to species level remains a challenge. Sequencing of housekeeping genes (gyrB, rpoB...) is considered the gold standard. However, these methods are costly and time-consuming. Pérez-Sancho et al. (2018) demonstrated the utility of MALDI-TOF MS (MT) for the identification of Aeromonas at the genus level, but accurate identification of the main species involved in fish diseases is not possible. The quality of the identification performed by MT depends on the associated database. Currently, the MT database proposed by Bruker contains reference spectra for only 22 of the 34 described species. Furthermore, the reference spectra are mainly performed for a single isolate per species, which reduces the consideration of intra-species diversity. Finally, the culture conditions used to create the spectra are not the same for all species and may be different from those used for the isolation of pathogenic species collected from fish for example.The objective of this study was to generate a new MT database including all 34 Aeromonas species, using culture conditions at 22°C for 48h and to test its accuracy on different species of interest. For each species, three reference spectra were generated to assess repeatability and reproducibility. A collection of 196 Aeromonas isolates (A. salmonicida n=78, A. bestiarum n=68, A. sobria n=27, A. popoffii n=20 and A. encheleia n=3) collected from fish and water samples and identified by sequencing of gyrB and rpoB genes were used to test the new database and also Bruker. Two sample preparation methods (direct deposit and after simple acid extraction using formic acid deposit) have been evaluated.Thanks to the new database, the identification of A. salmonicida and A. bestiarum species is improved in comparison with the Bruker database. These results provided depend on the deposit used. For A. popoffii, the result was less effective. For A. sobria and A. encheleia no mismatch were recorded.These first results confirm the possibility of using TM for the identification of Aeromonas species, provided that a suitable database is available.s.
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