Acne-like chronic inflammatory activity of Propionibacterium acnes preparations in an animal model: correlation with ability to stimulate the reticuloendothelial system.

The ability of strains and fractions of killed propionibacteria suspensions to produce chronic rat ear inflammation after intradermal injection of 70-micrograms aliquots was highly correlated with production of splenomegaly in the mouse after i.p. injection of 1.4 mg Propionibacterium acnes strains CN 6134, VPI 0009, ATCC 11828, and UCLA SC and N1 produced a 2- to 3-fold increase in rat ear thickness and a 5- to 7-fold increase in mouse spleen weight 15 days post injection. In contrast P. granulosum CN 5888, P. acnes UCLA 6S and periodated, acetylated, or 12-h cultures of VPI 0009 were inactive or weakly active as stimulators of chronic ear inflammation and splenomegaly. Active strains produced in the rat ear a transepidermal elimination response characterized by follicular encapsulation and the formation of secondary comedones. These effects correlated with persistence of phagocytized bacteria within macrophages. Furthermore, when rats were first immunized and then challenged with active strains of P. acnes, an increased sensitivity to low doses of P. acnes and a chronic exacerbation of inflammation was observed.