Abstract:

Objective To evaluate the effectiveness of matrix-assisted laser desorption ionization-time of flight mass spectrometry（MALDI-TOF MS） in identifying Corynebacterium and coryneform-like bacteria by comparing with API Coryne. Methods A total of 129 isolates of coryneform bacteria were collected from the clinical samples of 50 patients. The identification of Corynebacterium and coryneform-like bacteria was performed using MALDI-TOF MS based on direct on-plate extraction of formic acid and API Coryne,respectively. The isolates were identified with the cut-off scores（specie level ≥1.7,genus level ≥1.5 and no identification <1.5） for MALDI-TOF MS. The first 500 bp of the 16S rRNA gene of the above isolates was sequenced to determine the types of them. Results A total of 129 isolates of coryneform bacteria were isolated from the clinical samples of patients,and the first 500 bp of the 16S rRNA gene was sequenced. The results showed that 95 of them were Corynebacterium,covering 13 species,and 34 of them were coryneform-like bacteria,covering 15 genera. For MALDI-TOF MS bacterial identification,100% of Corynebacterium were identified as genus level,and 98.9% of them were identified as specie level. The 94.1% of coryneform-like bacteria were identified as genus level,and 88.2% of them were identified as specie level. However,API Coryne was able to identify 84.2% of Corynebacterium to the specie level and 61.8% of coryneform-like bacteria to the genus level. Conclusions MALDI-TOF MS based on formic acid direct on-plate extraction is more effective in identifying Corynebacterium and coryneform-like bacteria than API Coryne.

Key words: Corynebacterium, Coryneform-like bacterium, Matrix-assisted laser desorption ionization-time of flight mass spectrometry, API Coryne