Grouping of oral streptococcal species using Fourier-transform infrared spectroscopy in comparison with classical microbiological identification.

The grouping and identification made by Fourier-transform infrared spectroscopy (FT-IR) of 40 oral streptococcal strains was compared with their known taxonomic positions. Grouping was obtained by cluster analysis on the spectral distances between the first derivative spectra of the strains. Spectra were divided into five spectral 'windows' and cluster analysis was either on either a combination of all five windows or on a selected window. The oral streptococci were divided into two main clusters, mutans streptococci and other streptococci. This division was based mainly on the spectral information contained in the window between 1300-900 cm-1, indicative of polysaccharide and phosphate-carrying compounds. In the grouping based on the entire spectrum, species clusters could be observed for Streptococcus crista, Strep. salivarius and Strep. rattus. A few strains were placed in wrong clusters because of intra-strain variance. It is concluded that the grouping of these oral streptococcal species was good and similar to the classical taxonomy and that FT-IR might develop into a new identification method for oral streptococci.