Identification of seven species of the Lactobacillus acidophilus group by FT–IR spectroscopy

Fourier transform infrared (FT–IR) spectra of 102 strains of the seven species of the Lactobacillus acidophilus group were collected and investigated for their potential use in classification and identification on species level. The database built contains more than 370 spectra. Various procedures of pre-processing and classification methods have been compared with respect to their predictive ability. The most encouraging results were achieved with linear discriminant analysis (LDA) of the absorbance values of normalized spectra at selected wavenumbers. The rate of correct species assignment in cross-validation (Jackknife procedure with one spectrum left out for model building) were 95%, 95%, 69%, 100%, 88%, 100%, and 91% for L. acidophilus, L. amylovorus, L. crispatus, L. gallinarum, L. gasseri, L. helveticus, and L. johnsonii, respectively. Very distinct grouping was found for L. gallinarum and L. helveticus, the most difficult differentiation in LDA was between the pairs L. crispatus/L. amylovorus and L. gasseri/L. johnsonii.