Propionibacteria

Bacteria of the genus Propionibacterium, Gram-positive anaerobes best known for their role in dairy fermentations. Certain species convert lactic acid into propionic acid, acetic acid, and carbon dioxide, the reactions that create the characteristic eyes and nutty, sweet flavor of Swiss-type cheeses such as Emmental. Beyond cheese, they contribute to silage fermentation and are studied as probiotic candidates. Their metabolism is strictly anaerobic, so cheese makers manage curd handling and ripening conditions to favor their growth at the right stage. Other species are skin commensals, of no food significance but important in distinguishing contamination sources.