Background: In this study, we compared various methods of taxonomic identification of Bacillus strains: biochemical methods, 16S rRNA gene sequencing, and matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS). We also developed a pathogen- isolate resource database, thus increasing the identification rate when using MALDI-TOF MS.

Methods: Thirty Bacillus strains were obtained from the NCCP (National Culture Collection for Pathogens) and were identified using the VITEK 2 system (bioMérieux, France), API kit (bioMérieux, France), 16S rRNA gene sequencing, and MALDI-TOF MS. The pathogenicity of Bacillus cereus was confirmed through the identification of virulent genes using a multiplex PCR, and both protein extraction for protein profiling in MALDI-TOF MS and repetitive-sequence fingerprinting were performed.

Results: The identification rates at the species level were 40%, 80%, and 76.3% for the VITEK 2 system (bioMérieux), 16S rRNA gene sequencing, and MALDI- TOF MS, respectively. When the major spectrum- profiling dendrogram was compared with the phylogenetic tree, which was constructed based on the 16S rRNA gene sequences and rep-PCR fingerprinting, the classifications were confirmed to be effective.

Conclusion: Identification of Bacillus strains using MALDI-TOF MS was more effective than that using the VITEK 2 system (bioMérieux), but was similar to that using 16S rRNA gene sequencing. Continual addition to a proteome-based database can result in increased identification rates for MALDI-TOF MS. (Ann Clin Microbiol 2016;19:110-120)