General Information: This bacterium is the most common gram-positive, non-spore forming, anaerobic rod encountered in clinical specimens. The causative agent of acne, it typically grows as an obligate anaerobe. Some strains are aerotolerant, but still show better growth as an anaerobe. It has the ability to produce propionic acid, as its name suggests. It also has the ability to produce catalase along with indole, nitrate, or both indole and nitrate. Propionibacterium resembles Corynebacterium in morphology and arrangement, but is non-toxigenic. It is a common resident of the pilosebaceous (hair follicle) glands of the human skin. The bacteria release lipases to digest a surplus of the skin oil, sebum, that has been produced. The combination of digestive products (fatty acids) and bacterial antigens stimulates an intense local inflammation that bursts the hair follicle. Since acne is caused in part from an infection, it can be suppressed with topical and oral antibiotics such as clindamycin, erythromycin, or tetracycline.