ABSTRACT
Propionibacteria are Gram-positive, high G%+C%, mesophilic, aerotolerant, pleomorphic rods belonging to the Actinobacteria class (Stackebrandt et al., 2006). The Actinobacteria are able to exhibit a wide range of morphologies and physiological and metabolic properties, and can colonize various niches including soil. The Propionibacterium genus currently comprises 12 species and has been distinguished into 2 distinct groups based on their natural biotopes as dairy (or classical) and cutaneous propionibacteria. The species of the cutaneous group are usually isolated from the skin and the gastrointestinal tract of humans and animals, while the species of the classical group have been mainly isolated from raw milk, fermented dairy products, fermented vegetables, and silage. Dairy propionic acid bacteria (PAB) have been traditionally isolated from milk and dairy products, and the four typical dairy species identi-ed are Propionibacterium freudenreichii, Propionibacterium acidipropionici, Propionibacterium jensenii, and Propionibacterium thoenii (Thierry et al., 2011).
