Because of the high degree of similarity observed for the 16S rRNA gene sequences among strains belonging to Lactobacillus casei, Lactobacillus paracasei, and Lactobacillus rhamnosus, these three species are commonly referred to as the L. casei group. Species belonging to the L. casei group may be isolated mainly from milk and dairy products, but also from fermented sausages, vegetables, wine, and, occasionally, from sourdough. Besides food items, strains of the L. casei group may be isolated from human reproductive and gastrointestinal tract and stools, which accounts for their large use as probiotics.