To improve the existing methods based on phenotype and/or genotype a new genotyping method was investigated to identify Lactobacillus species. / The method used the polymerase chain reaction (PCR) to amplify specific sequences of aminopeptidase (pepN) genes. The primers for the PCR reactions derived from a pepN sequence of Lactobacillus rhamnosus S93. PepN amplification products of 387 bp were obtained from forty three Lactobacillus strains and from some strains of Lactococcus (3), Streptococcus (2) and Bifidobactertium (5). / Restriction fragment length polymorphisms (RFLPs) and single-strand conformation polymorphisms (SSCP) methods were used to detect polymorphisms among amplified aminopeptidase DNA fragments from the different Lactobacillus strains. / The results of RFLPs after digestions with Sau3A I, Rsa I and Tru9 I confirmed that the PCR products were specific. According to the fingerprints generated, Lactobacillus species tested could be grouped in four. / SSCP allowed a good discrimination between different pepN PCR products of the same size. Some Lactobacillus strains, Lb. plantarum and Lb. rhamnosus showed the different ssDNA patterns. Though for many strains of Lactobacillus the SSCP patterns were similar, no general comparison can be made because all the samples were not loaded on the same SSCP polyacrylamide gel. The SSCP, PCR-based method can be easily modified to increase the rate of polymorphism detection. / This new genetic identification method is different from others because it uses specific pepN DNA sequences for each strain tested and it uses SSCP to detect the presence of polymorphisms. The method is also applicable to other genera of lactic acid bacteria.

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