Multivariate statistical methods for discrimination of lactobacilli based on their FTIR spectra

In this study, 41 strains belonging to 6 Lactobacillus species originating from culture collections, and isolates from homemade cheese that had previously been genetically classified, were discriminated based on their FTIR spectra. The lactobacilli species L. brevis, L. diolivorans, L. plantarum and L. rhamnosus could be differentiated on the basis of their FTIR spectra by applying multivariate statistical techniques (Hierarchical Cluster Analysis, Principal Component Analysis and Multidimensional Scaling). The strains belonging to L. paracasei and L. casei could not be separated from each other, and formed one group that was distanced from the other investigated species. The combination of common multivariate statistical methods used for the analysis of FTIR spectra could provide a powerful method for discrimination and even the identification of lactobacilli on a species level. The strains and subspecies within the lactobacilli species could not be differentiated by applying multivariate exploratory statistical methods. The FTIR spectra of lactobacilli were robust against the variation in the consistency of the growth medium (broth or agar medium of the same composition), applied spectroscopic techniques (KRS-5 or tablets) and the recorded biomass quantities of 2 and 3 mg. Furthermore, the distances between the two spectra of the same selected strain, which were sampled ca. 12 months apart, were insignificant.Abstract(FTIR) 6 41 (L. brevis), L. diolivorans (L. plantarum), (L. rhamnosus) FTIR (L. paracasei) (L. casei) FTIR FTIR (KRS-5 (2 mg 3 mg) 12RésuméDans cette étude, 41 souches appartenant à six espèces de Lactobacillus provenant de collections de cultures ou isolées de fromages faits maison, précédemment classées génétiquement, sont discriminées selon leur spectre infrarouge à transformée de Fourier (IRTF). Les espèces Lactobacillus brevis, L. diolivorans, L. plantarum et L. rhamnosus peuvent être différenciées à partir de leur spectre IRTF en appliquant des techniques statistiques multidimensionnelles (classification ascendante hiérarchique, analyse en composantes principales et positionnement multidimensionnel). Les souches de L. paracasei et L. casei ne peuvent pas être séparées entre elles et forment un groupe distant des autres espèces étudiées. La combinaison de méthodes statistiques multidimensionnelles, couramment utilisées pour l’analyse de spectres IRTF, peut fournir une méthode puissante pour la discrimination et même l’identification de lactobacilles à l’échelle de l’espèce. Les souches et sous-espèces parmi les espèces de lactobacilles ne peuvent pas être différenciées en appliquant des méthodes statistiques multidimensionnelles exploratoires. Les spectres IRTF des lactobacilles sont robustes quels que soient les changements de consistance des milieux de culture (milieu liquide ou gélosé de la même composition), les méthodes spectroscopiques appliquées (KRS-5 ou comprimé) ou la quantité de biomasse analysée (2 ou 3 mg). De plus, la distance entre deux spectres d’une même souche sélectionnée, échantillonnée avec 12 mois d’écart, est insignifiante.

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