The First Evidence of Bacterial Foci in the Hair Part and Dermal Papilla of Scalp Hair Follicles: A Pilot Comparative Study in Alopecia Areata

The role of the microbiome in hair follicle (HF) growth represents a growing field of research. Here, we studied the bacterial population in the scalp hair follicles of subjects with alopecia areata (AA). Two Healthy and two AA subjects, respectively (20-60 years old), were enrolled and studied regarding the microbial community in the subepidermal scalp compartments by means of a 4-mm biopsy punch. Samples were examined by 16S sequencing, histochemical staining (Gram's method), and transmission electron microscopy (TEM). Bacterial foci were observed in the AA subjects' follicles with both the two adopted complementary approaches (electron microscopy and Gram staining). Significant (p < 0.05) differences were also found in the three-layer biopsy samples (p < 0.05) regarding the bacterial population. In particular, in the deep epidermis and dermis levels, a significant (p < 0.05) lower abundance of Firmicutes and a higher abundance of Proteobacteria were found in AA samples compared to the healthy control. Firmicutes also showed a significant (p < 0.05) lower abundance in hypodermis in AA subjects. In addition, Enterobacteriaceae and the genera Streptococcus, Gemella, Porphyromonas, and Granulicatella were relatively more abundant in AA groups at the deep epidermis level. The Staphylococcus and Flavobacterium genera were significantly less abundant in AA samples than in controls in all three-layer biopsy samples (p < 0.05). In contrast, Veillonella and Neisseriaceae were relatively more abundant in the healthy control group compared to the AA sample. Therefore, higher alpha diversity was observed in all three-layer biopsy samples of AA patients compared to the control. In conclusion, our data suggest that tAA could be defined as a "hair disease associated with dysregulated microbiome-immunity axis of hair follicles".