49 - The Cutaneous Propionibacteria

Abstract

Propionibacteria are Gram-positive, non-motile rods with typical coryneform appearance. The genus Propionibacterium may conveniently be subdivided into the classical propionibacteria associated with dairy products, and the cutaneous propionibacteria associated with human skin. This chapter focuses on Propionibacterium acnes (P. acnes), P. avidum, P. granulosum, P. propionicum, and P. lymphophilum, which are found as commensals on human skin and other keratinized epithelia. In the majority of adults, large and relatively stable populations of propionibacteria dominate the micro flora on the surface and in the pilosebaceous follicles of sebum-rich areas of skin. As part of the normal cutaneous microflora, propionibacteria function to help maintain the ecosystem of the skin. Thus, in healthy adults propionibacteria are a benign presence displaying very low levels of virulence. Understanding of the interactions between the cutaneous propionibacteria and their human host is inadequate, in spite of investigations over many years. The taxonomic situation of propionibacteria is unlikely to change in the near future, apart from detailed analysis with molecular techniques to determine the variance within the species. The use of propionibacteria as anticancer vaccines remains uncertain, not only because of their variable success but also because of developments in other areas for cancer treatment.