Gram-positive, anaerobic, non-spore forming, rod-shaped (bacillus) prokaryote. Inside silos crops ferment and substances produced in the fermentation process protects the silage from spoilage by yeasts and molds. This bacterium is often used as a bacterial inoculant to improve the aerobic stability of silage (such as grain, grass and legumes). Propionibacteria are unique in their ability to ferment erythritol (a natural sugar alcohol) or glucose to propionic acid and acetic acid. Some species of Propionibacteria are found in food products such as cheeses and other dairy products. P. freudenreichii is used in Swiss cheese manufacturing to produce its flavor and characteristic holes. The flavor derives from propionate (propionic acid), a product of the fermentation and the holes in Swiss cheese from bubbles of carbon dioxide. Proprionibacteria bacteria are found as saprophytes in humans, animals, dairy products and grain. Proprionibacteria are part of the normal flora of skin. P. acnes causes acne or acne vulgaris. Some Propionibacteria strains synthesize nitric oxide (NO) from nitrate reduction. Nitric oxide production is believed to be the mechanism by which some probiotics improve the mucosal barrier in mammals.