Evaluation of conventional methods for species identification of Staphylococcus aureus using MALDI-TOF MS, protein identification and quantification

Abstract

Objectives: This study aimed to evaluate conventional methods for species identification of Staphylococcus aureus by MALDI-TOF MS. Additionally, the representatives of different species were used to analyze protein expression. Materials and methods: A total of 185 non-duplicated clinical S. aureus identified using the conventional method (colony morphology, Gram’s stain, slide coagulase test, tube coagulase test, catalase test, and mannitol fermentation) was confirmed the identification by MALDI-TOF MS and analyzed by Mass spectral profiling (MSP) and Principal component analysis (PCA). The representatives of different species reported by both methods were confirmed using 16SrRNA sequence and analyzed proteins expression by timsTOF MS. Results: All S. aureus suspected isolates could discriminate among species by MALDI-TOF MS including S. aureus (N=151, 81.6%), S. argenteus (N=32, 17.3%), S. hominis (N=1, 0.5%), and S. haemolyticus (N=1, 0.5%). Using 16S rRNA genebased analysis, S. aureus and S. argenteus could not differentiate from each other. Protein expression of S. aureus was similar to S. argenteus. These genes including rpsT, Huti, pyrF, atpD.1, cpfC, SAUA300_0786, atl.1, and MW2416 showed higher expression in S. aureus (MS076) than S. argenteus (MS060), S. haemolyticus (MS095) and S. hominis (MS060). Conclusion: MALDI-TOF MS provides an excellent tool for accurately species identification of staphylococci. S. aureus expressed protein analyzed higher than the other 3 species. The highest protein expression in S. aureus implies the most virulence of this strain.