Propionibacterium

Abstract

The genus Propionibacterium is currently composed of the following 11 species: P. Freudenreichii (P. Freudenreichii subsp. Freudenreichii and P. Freudenreichii subsp. Shermanii), P. Jensenii, P. Thoenii, P. Acidipropionici, P. Cyclohexanicum, P. Microaerophilum, P. Acnes, P. Avidum, P. Granulosum, P.australiense, and P. Propionicum. The species Propionibacterium lymphophilum and Propionibacterium innocuum, previously described as part of the Propionibacterium genus, have now been reclassified within the family Propionibacteriaceae as Propionimicrobium lymphophilum and Propioniferax innocua, respectively.1,2 Bacteria within the Propionibacterium genus are gram-positive, anaerobic-to-aerotolerant-to-microaerophilic, nonspore-forming pleomorphic rods. They are 0.2–1.5 μm in diameter × 1–5 μm in length and have a high G + C content [57–68 mol% (Tm)]. They can appear diphtheroid or club shaped, with one end rounded and the other tapered or pointed, but may also be coccoid, bifid, branched, or filamentous with lengths of up to 20 μm.3 Propionibacteria are chemoorganotrophs with complex nutritional requirements and produce large amounts of propionic and acetic acids, and lesser amounts of isovaleric, formic, succinic or lactic acids, and carbon dioxide as the end products of their fermentation reactions.3 Although predominantly anaerobic, most propionibacteria are catalase positive. Tetrahydrogenated menaquinones with nine isoprene units [MK-9(H4)] are the major respiratory quinones. Their optimal growth temperature is between 30°C and 37°C, and on solid media colonies will appear smooth, rough, or convex, and may be white, grey, pink, red, yellow, or orange in color.3