Development and evaluation of MALDI-TOF MS-based serotyping for Streptococcus pneumoniae

Surveillance of Streptococcus pneumoniae serotypes is important for the successful implementation of vaccination strategies to prevent the spread of invasive pneumococcal diseases. The standard method of serotyping of pneumococcal isolates is the phenotypic Neufeld test, which is cost- and labor-intensive. Recently, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) has been implemented as a rapid, simple and inexpensive method for identifying species. We evaluated the performance of MALDI-TOF MS for serotyping ten major serotypes of S. pneumoniae in Japan (serotypes 3, 6B, 15A, 15C, 19A, 19 F, 23A, 24 F, 35B and 38) using the Biotyper and ClinProTools. After optimizing the settings, we validated their serotyping performance for serotypes 3, 15A and 19A using a separate set of isolates that were not used in the creation of the classification algorithms. A total of 574 isolates of S. pneumoniae collected from Japanese nationwide surveillance studies were included. Of these, 407 isolates belonged to the ten major serotypes. Biotyper and ClinProTools correctly identified 77.9 % and 84.0 %, respectively, of the ten major serotype isolates. The validation analysis included a total of 113 isolates of the serotypes 3, 15A and 19A isolates. Biotyper and ClinProTools correctly identified 85.0 % and 69.9 % of the validation cohort isolates, respectively. MALDI-TOF MS has the potential to discriminate the ten major S. pneumoniae serotypes prevalent in Japan.