Delayed skin test reactivity to Propionibacterium acnes correlates with severity of inflammation in acne vulgaris.

Propionibacterium acnes is the bacterial species most consistently isolated from acne lesions. Intradermal injection of a heat-killed suspension of P. acnes induced a delayed erythematous and often popular inflammatory reaction which was maximal after 24-48 h. This response was dose related and was probably mediated at least partly by immune mechanisms. In eighty-one subjects with acne of varying severity of the acne. These findings indicate that the host response to P. acnes is an important variable in determining the severity of inflammatory acne.