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Lactobacillus plantarum, Lactobacillus pentosus, and Lactobacillus paraplantarum (M.-C. Curk, J.-C. Hubert, and F. Bringel, Int. J. Syst. Bacteriol. 46595498, 1996) can hardly be distinguished on the basis of their phenotypes. Unlike L. plantarum and L. paraplantarum, L. pentosus ferments glycerol and xylose but not melezitose. We identified two L. pentosus strains (CNRZ 1538 and CNRZ 1544) which ferment glycerol and melezitose but not xylose. a-Methyla-mannoside was fermented by 66% of the L. plantarum strains tested but not by L. paraplantarum strains. In this paper we describe a simple method to identify L. plantarum, L. pentosus, and L. paraplantarum. This method is based on nonradioactive Southern-type hybridization between BglI DNA digests of the lactobacilli tested and a DNA probe (L. plantarum pyrDFE genes from strain CCM 1904). A total of 68 lactobacilli were classified into five groups on the basis of the bands detected. Two groups contained L. plantarum strains; one of these groups contained 31 strains, including the type strain, and was characterized by bands at 7,4, and 1 kb, and the other group contained strain LP 85-2 and was characterized by bands at 5 and 1.1 kb. Only one band (a band at around 7 kb) was detected in the strains belonging to the L. pentosus group, and two bands (at 4 and 1 kb) were found in the strains belonging to the L. paraplantarum group. No hybridization was detected in the last group, which contained Lactobacillus casei, Lactobacillus coryniformis, Lactobacillus paracasei, Lactobacillus brevis, Lactobacillus delbrueckii, and Lactobacillus leichmannii strains.Lactobacilli related to Lactobacillus plantarum are lactic acid bacteria that are important in many plant fermentations (silage, pickled vegetables, sourdough) and meat and fish fermentations (17). Some of these organisms, such as the organisms found in beer, also can be food spoilage agents (19), and some lactobacilli are also found in cavities of mammals (16).The taxonomy of L. plantarum is not satisfactory (13); this species contains strains that have similar biochemical characteristics but exhibit little similarity at the DNA level. Dellaglio et al. (9) identified the following three groups on the basis of DNA-DNA hybridization data: L. plantarum, Lactobacillus pentosus, and an atypical L. plantarum group recently reclassified as Lactobacillus paraplantarum (7). In agreement with the results of Dellaglio et al. (9), Zanoni et al. (24) revived the name L. pentosus for a distinct taxon; L. pentosus can be distinguished from L. plantarum by its ability to produce acid from D-xylose and glycerol (10,13). However, these phenotypic characteristics are not sufficient to distinguish L. plantarum from L. pentosus since some strains ferment glycerol but not D-xylose (this study) or D-xylose but not glycerol (16). Direct sequencing of 16s rRNAs by reverse transcription clarified the phylogenetic status of several groups of lactic acid bacteria but could not be used to distinguish L. plantarum from L. pentosus since the 16s ...