Identification of a variety of Staphylococcus species by matrix-assisted laser desorption ionization-time of flight mass spectrometry

Abstract

Whole-cell fingerprinting by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS) in combination with a dedicated bioinformatic software tool (MALDI Biotyper 2.0) was used to identify 152 staphylococcal strains corresponding to 22 staphylococcal species. Spectra of the 152 isolates, previously identified at the species level using a sodA gene-based oligonucleotide array, were analyzed against the main spectra of 3,030 microorganisms. A total of 151 strains out of 152 (99.3%) were correctly identified at the species level; only one strain was identified at the genus level. The MALDI-TOF MS method revealed different clonal lineages of Staphylococcus epidermidis that were of either human or environmental origin, which suggests that the MALDI-TOF MS method could be useful in the profiling of staphylococcal strains. The topology of the dendrogram generated by the MALDI Biotyper 2.0 software from the spectra of 120 Staphylococcus reference strains (representing 36 species) was in general agreement with that inferred from the 16S rRNA gene-based analysis. Our findings indicate that the MALDI-TOF MS technology, associated with a broad-spectrum reference database, is an effective tool for the swift and reliable identification of Staphylococci.

FIG. 1.

Classification of staphyloccal reference strains. Shown is a score-oriented dendrogram of staphylococcal reference strains included in the database. The terms “500-level cg” and “750-level cg” define cluster groups (cg) based on the branching pattern using critical distance levels of 500 and 750, respectively. ^#, cluster groups as defined by the phylogenetic analysis of 16S rRNA genes.

FIG. 2.

Score-oriented dendrogram of clinical (C) and environmental (E) S. epidermidis isolates.