Propionibacterium species and follicular keratinocyte activation in acneic and normal skin

Background The pathogenesis of acne vulgaris is multifactorial with increased sebum production, alteration in the quality of sebum lipids, dysregulation of the hormone microenvironment, follicular hyperkeratinization and Propionibacterium acnes-driven inflammation as major contributory factors. Hyperproliferation of keratinocytes is believed to contribute to hypercornification and eventually leads to comedone development. While the distribution of P. acnes is relatively well documented in acneic and healthy skin, little is known about P. granulosum and P. avidum. Objectives To visualize directly the three major Propionibacterium in 117 control and 26 acneic skin samples. In addition, keratinocyte proliferation was evaluated. Methods Propionibacteria were visualized by immunofluorescence microscopy, and keratinocyte proliferation was assessed by Ki67, keratin (K) 16 and p63 immunochemistry. Results P. acnes was identified in 68 samples (48%), while P. granulosum was identified in 12 (8%) samples; P. avidum was not detected at all. Unexpectedly, acne samples did not show higher keratinocyte proliferation than controls, nor was there any association between bacterial colonization and expression of Ki67/K16/p63. Conclusions Our findings do not support earlier notions of follicular keratinocyte hyperproliferation as a cause of ductal hypercornification in acneic facial skin. Further studies on the mechanisms underlying hypercornification in acne pathogenesis are needed.