Mode and Structure of the Bacterial Community on Human Scalp Hair

Bacterial communities on various parts of the human body are distinct. We were the first to report the existence of a stable bacterial community on human scalp hair and demonstrated that an analysis of its structure by terminal restriction fragment length polymorphism (T-RFLP) is helpful for individual discrimination. However, the ecology of the bacterial community on human scalp hair has not yet been elucidated in detail. We herein investigated the mode, quantity, and phylogeny of bacterial communities on the human hair shaft and root and showed the results obtained from one representative individual. Direct SEM observations of hair, without a pretreatment, confirmed the ubiquitous presence of bacteria-like coccoids and rods on the shaft and root of hair from the human scalp, with 10⁵-10⁶ cells cm^-2 of hair and 10⁷ cells cm^-2 of hair, respectively. These values corresponded to the 16S rRNA gene copy numbers obtained by qPCR. These numbers were not significantly affected by detergent washing. These results represented those obtained from many individuals with different hair lengths, ages, and gender. The major OTUs on the human scalp hair shaft and root were the same and included two species of Pseudomonas (phylum Proteobacteria), Cutibacterium and Lawsonella (phylum Actinobacteria), and Staphylococcus (phylum Firmicutes). These results suggest that major bacteria on the human hair shaft are indigenous and derived from the hair root.