Identification of Lactobacillus Strains Present in Fermented Dairy Products and Their Differentiation Using Molecular Methods

Lactobacilli constitute an important group of non-pathogenic Gram-positive bacteria commonly found in foods like dairy products, beverages, fruits, vegetables and fermented meat as well as used in the preservation of plant-originated foods and feeds. Members of the genus Lactobacillus are also present in human and animal gastrointestinal (GI) and urogenital tract [Tannock 1995]. Lactobacilli, as beneficially affecting health and functions of GI tract as well as because of their technological properties, have been widely used in dairy industry and in probiotic diet supplement production. Lactobacillus species most frequently found in dairy products are L. acidophilus, L. casei/ L. paracasei, L. rhamnosus, L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis and L. helveticus [Andrighetto et al., 1998; Couret et al., 2004; Guidemonde et al., 2004; Tannock et al., 1999]. Conventional biochemical and physiological tests have some limitations in discriminating large numbers of isolates showing similar physiological characteristics [Berthier & Ehrlich, 1999]. Therefore, many studies have focused on the application of molecular biology techniques for the rapid identification and differentiation of lactobacilli [Andrighetto et al., 1998; Zhong et al., 1998]. Nowadays the rRNA genes have been generally accepted as the potential tools for the identification and phylogenetic analysis of the bacteria [Song et al., 2000; Ward et al., 2005]. Investigations aiming to get new strains of outstanding probiotic features result in a large number of isolates. In this context, some important points remain to be considered for an objective selection of strains of interest: (i) rapid classification and identification of unknown isolates; (ii) evaluation of genetic diversity among strains and the impact of diversity on the relevant properties of microorganisms; and (iii) strain typing to assess genetic stability over time [Berthier & Ehrlich, 1999]. Moreover, identification of bacteria at a strain level is necessary in the case of applying selected strains in industry for the protection of patented strains property. In turn, strains incorrectly classified and without proper genetic discrimination make standardization of the production and the classification of products as probiotic impossible. In the present study we applied molecular techniques in order to verify phenotypic identification and differentiate Lactobacillus isolates in reference to type strains. Moreover, a preliminary assessment of the usefulness of typing methods for rapid strain discrimination has been made.