Effect of two kinds of bacterial pretreatment methods on the clinical isolate strains identification by MALDI-TOF MS

Abstract

Objective To evaluate the effect of different pretreatment methods on the identification of clinical bacterial isolates by matrix assisted laser desorption ionization time of flight mass spectrometry (MALDI-TOF MS). Methods Forty-three clinical isolates were collected and subcultured before treated by two different sample preparation methods including off-plate extraction method and direct on-plate method. And then the treated strains were identified by MALDI-TOF MS. The identification accuracy of the two methods and the peak of protein fingerprint were compared. Results Using the results of 16S rRNA or ITS RNA as reference standard, the identification rates of gram positive bacteria, gram negative bacteria and fungus treated by off-plate extraction method were 93.8%, 100% and 30.8%, respectively. And the identification rates of gram positive bacteria, gram negative bacteria and fungus treated by direct on-plate extraction method were 75.0%, 100% and 7.7%, respectively. The characteristic peak in the protein fingerprint obtained after extraction was more; the signal-to-noise ratio was higher and the reproducibility of protein fingerprint was better. Conclusion It is recommended that the off-plate extraction method for MALDI-TOF identification should be used, which is of great clinical significance for the establishment of a standard microbial detection process and the improvement of the accuracy of mass spectrometry identification. Key words: Matrix-assisted laser desorption/ ionization time of flight mass spectrometry; Protein fingerprint; Pretreatment; Off-plate extraction method; Direct on-plate method