Rapid discrimination of lactobacilli isolated from kefir grains by FT-IR spectroscopy

Fourier transform infrared (FT-IR) spectroscopy was used in combination with multivariate statistical analysis for differentiation of lactic bacteria isolated from kefir grains. Twelve reference strains and 42 lactobacilli isolates from four local kefir grains, previously identified by biochemical traditional techniques at species level were included in this study. The spectra were analysed by hierarchical clustering analysis (HCA) using Pearson's product-moment correlation coefficient and Ward's algorithm. The differentiation between homo- and heterofermentative lactobacilli, proposed as a first level in the classification scheme, was performed with vector normalized first derivatives spectra in the windows 1789-1700, 1059-935, 3000-2927 and 896-833 cm(-1). For heterofermentative lactobacilli the windows 1780-1750, 1500-1200, 2950-2930 and 900-700 cm(-1) were found to contribute to the maximal separation among L. kefir, L. parakefir and Lactobacillus brevis. It was also demonstrated that although this model was robust against small variations in growth temperature (+/-5 degrees C) and growth time (+/-5 h), the make of culture medium used (Biokar or Difco) affected the separation of heterofermentative lactobacilli at species level. For homofermentative lactobacilli the spectral regions 1230-900, 1777-1690, 1357-1240 and 2960-2870 cm(-1), were selected for discrimination among 5 different species that are normally present in kefir grains: L. plantarum, L. acidophilus, L. kefirgranum, L. kefiranofaciens and L. cassei. The classification and discrimination schemes proposed in this work completely matched with the identification obtained by classical biochemical techniques at species level.