Surface-enhanced Raman scattering as a discrimination method of Streptococcus spp. and alternative approach for identifying capsular types of S. pneumoniae isolates

The surface-enhanced Raman spectroscopy (SERS) is a method known for its effectiveness in detecting and identifying microorganisms, that was employed to differentiate various bacterial strains both at genus and species level. In this work, we have examined five species belonging to Streptococcus genus, namely S. pneumoniae, S. suis, S. pseudopneumoniae, S. oralis, and S. mitis. Additionally, we conducted SERS experiments on ten S. pneumoniae strains, representing different capsular types. In all of cases we obtained unique SERS signals being spectroscopic fingerprints of bacterial strains tested. Moreover, the principal component analysis (PCA) was performed in order to prove that the spectra of all studied strains can be well separated into five (in case of streptococcal strains) or ten (in case of pneumococcal serotypes) groups. In both investigated situations, the separation at the level of 95% was achieved, proving that SERS-PCA-based method can be used for reliable and fast identification of different strains belonging to the Streptococcus genus, including encapsulated pneumococcal isolates. [Display omitted] •The SERS-based classification of the capsular types of pneumococcal isolates has been presented for the first time.•The differences between streptococcal serotypes, connected with their biochemical structure, are visible in the SERS spectra.•SERS-PCA technique allowed to distinguish S. pneumoniae cells belonging to different capsular types with 95% of accuracy.•The SERS studies of the capsule of S. pneumoniae are crucial in fast and reliable identification of pneumococcal diseases.