Propionibacterium is a Gram-positive, anaerobic genus named for its characteristic production of large amounts of propionic acid. First described by Orla-Jensen in 1909, the genus is typically divided into two principal groups, the classical or dairy propionibacteria and the cutaneous propionibacteria or acne group strains. Both groups serve well-known, though very different functions. The classical group is often used in production of dairy products, particularly swiss cheese and other natural fermentations, while the acne group strains is a normal inhabitant of human skin and elsewhere on the body involved in causing acne vulgaris and other bacterial infections (Cummins and Johnson, 1986).