Relationship between the bacterial community structures on human hair and scalp

Abstract

In this study, we investigated and compared characteristics of the bacterial community structures on hair (scalp hair) and scalp in 18 individuals. Significant differences were found between the sites, in terms of cell density, alpha and beta diversity, and relative abundance of the phyla, Firmicutes and Proteobacteria, whereas no difference was found in relative abundance of the phylum Actinobacteria. Bacteria of the genus Cutibacterium showed similar relative abundance at both sites, whereas those of genus Pseudomonas were highly abundant on hair, and those of genus Staphylococcus were significantly lesser in abundance on hair than on scalp. Statistical correlations between the sites were high for the individual relative abundance of five major operational taxonomic units (OTUs). This suggests that the bacterial community structure on hair is composed of hair-specific genus, Pseudomonas, and skin-derived genera, Cutibacterium and Staphylococcus, and is distinguishable from other human skin microbiomes.

Host factors that shape the bacterial community structure on scalp hair shaft

“…Thirdly, we confirmed that the average bacterial cell number per cm 2 of scalp hair shaft was stable at approximately 3.5 (± 7.6) × 10 5 by estimating the 16S rRNA gene copy number (Table 2 ), which was consistent with that obtained in previous studies 16 , 17 , 22 . These results suggest that scalp hair shafts have a load of 10 5 bacterial cells without exception, and that shampooing or chemical treatment of scalp hair shaft would not significantly affect the total cell number (Table 4 ).…”

“…Recent studies of the human microbiome on scalp hair have shown that bacterial community structure varies between individuals and is distinguishable from that of other human skin microbiomes 14 – 17 . This study provided the first insights into the factors that contribute to the formation of bacterial community structures on scalp hair shaft.…”

“…To the best of knowledge, a relationship between environments of scalp skin and bacterial community structure between genders has not been reported. Because many bacterial species were reported to be shared between scalp skin and scalp hair shaft 17 , these environmental differences of scalp skin may be related to microbial differences in scalp hair shaft. Further research on intrinsic factors showed no difference in the cell numbers of major bacterial genera with respect to age and ethnicity (Supplementary Table S2 ).…”

“…Tridico et al analysed bacterial community structures on pubic and scalp hair and showed that they were only different in females 14 . We have previously reported the special features of bacterial community structures on scalp hair 15 – 17 . A specific individual bacterial community structure on scalp hair could be identified using the terminal restriction fragment length polymorphism method 15 .…”

“…Furthermore, we analysed the bacterial community structure on portions of human scalp hair shafts and roots from six individuals, using 16S amplicon sequencing, and found that the major bacteria on human scalp hair shafts are indigenous and derived from hair roots 16 . In a comparative analysis of bacterial community structures on scalp hair shaft and scalp skin, scalp hair shaft contained the hair-specific genus, Pseudomonas , and the skin-derived genera Cutibacterium and Staphylococcus , which were distinguishable from other human skin microbiomes 17 . These studies piqued our interest in why the bacterial community structure on scalp hair shaft is distinguishable, and different from that on the scalp skin.…”