Identification of Staphylococcus warneri from rainbow trout (Oncorhynchus mykiss Walbaum, 1792) using proteomics–based MALDI–TOF MS

Staphylococcus warneri, an opportunistic pathogen, is a causative agent of mortal diseases in rainbow trout farming (Oncorhynchus mykiss), which are of great economic value for Türkiye. In this study, in addition to traditional phenotypic, biochemical, histopathological and genetic methods, a high throughput proteomics based Matrix Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI–TOF MS) method was performed for precise identification of S. warneri. Fourteen isolates obtained from skin, gills, liver, spleen and kidney of a total of fifty diseased fish were phenotypically confirmed as S. warneri using the BBL CrystalTMGP identification system. Only 43% of these isolates showed positive PCR amplification for the 16S rRNA and sodA (superoxide dismutase A) gene, while 100% were identified as S. warneri by MALDI–TOF MS technique with high mass score value (m/z) between 2.35 and 3.05. From the comparative data obtained, it was concluded that MALDI–TOF mass spectrometry analysis can be recommended for the definitive confirmation of S. warneri, which showed indistinguishably close similarities with 16S rRNA gene sequences and sodA PCR results. To the best of knowledge, this is the first report to validate the results of phenotypic, biochemical, genetic and histological methods by the MALDI–TOF MS and shows that this is a successful identification approach, providing a high mass score (m/z) with 100% matching for accurate and faster identification of S. warneri. This promising diagnostic technique can identify many different bacterial fish pathogens, although a larger protein mass database for aquatic organisms is needed.